Stella, there are several distinctly different women's step through Frame Sizes available in the ancient SCHWINN Collegiate of the 1970's.
There are the 17 INCH frame size, and the 19 INCH frame size, and the 21 INCH frame size. THE 17 INCH frame size of the ancient Schwinn Collegiate would likely be perfect for a petite lady that is less than or equal to 5 foot one inch in height.
If you take a look around and ask old folks who might have a seventies era Collegiate in their shed or garage, you likely can find one gathering dust for maybe as much as perhaps $50 or perhaps Free if you're lucky. Sure, you will need to replace the tires and the tubes, & brake pads........ You likely will not need to replace the cables unless the bike is in rough shape with rust. Still, the BELL Pitcrew 600 cable set can be purchased at many Walmart stores for $10 and at Walmart.com and at Ace Hardware website, as it is not in Ace stores....only online. The Bell Pitcrew 600 cable set includes brake and shift cables and ferrules for handbrake levers.......YOU WILL NEED TO BUY OR BORROW or otherwise obtain a Brake CABLE CUTTER........you can get a decent enough one for about $16 to $17 with free shipping from several ebay store sellers. It is vital that you use a proper CABLE CUTTER that makes clean cuts in the cable and the housing too. Alternatively, you could try using a Dremel with a cut-off wheel, but I find that the Cable Cutter makes quick clean cuts with no effort. I have done about twenty bicycles with this $16 tool and it still cuts perfectly. That is not to say that this $16 tool will last as long as the same type of tool that looks the same but costs four times as much, but if you're not planning to replace all the cables on fifty to a hundred and fifty bicycles, then you will get your money's worth as you likely won't wear it out that it becomes too dull to continue to make perfect clean cuts. As far as locating a 17 inch ancient Collegiate frame, if you already have on hand some other sized men's or women's ancient Collegiate bike..........there is a guy in michigan on thE bay that is called ( trading_old_stuff) with 100% rating that routinely parts-out SCHWINN lightweights of the seventies and sixties.........he always has a bunch of parted Women's frames with front fork (Collegiates/Varsities/Suburbans) for about $10 to $12 each and probably as much as $35 shipping for the frame....... just one example....... Note that the very nice paint/ decal frames sell nearly immediately where the average or below average paint color/decal condition frames remain available for a long time..... Still, if you cannot locate something small enough, maybe purchasing a 17" frame from him or somebody else will allow you to build the 17 inch frame if you obtain another donor Collegiate. Heck, even if you find that the paint color and decals aren't presentable enough from his current inventory......................you could paint the frame with RUSTOLEUM from can with foam brush and/or bristle brushes --or-- with rattle cans of spray paint RUSTOLEUM 2X or Rustoleum, or tractor-farm implement spray paints from Tractor Supply or off the shelf Auto touch up spray paint from Advance Auto/Autozone/O'Reilly's/NAPA/Pep Boys....etc. Painting a bare frame is not too difficult. JUST BE AWARE THAT THERE ARE SIGNIFICANT DIFFERENCES IN THE STEM SIZING NEEDED FOR Schwinn frames from 1965 (22.2) to 1966 and later (21.1). Schwinn engineers made the wall thickness of the head tube thicker & stronger for 1966 model....this is why the stem size thickness is 21.1 for 1966 onward. There are millions of both stem sizes so there is no reason to worry about sourcing the part but you must remember that you need the correct size as 1965 & earlier WILL NOT FIT 1966 onward and vice-versa. The best Collegiate models are the 1970 through 1977 before FFS. 1969 and earlier has French made model F freewheel with 28-14 gearing and Huret Allvit rear derailleur. 1970 has the Shimano built GT-100 rear derailleur, and 32-14 gearing of the Japanese made model J freewheel. You get much better hill climbing with the 32 tooth 1st gear and the Shimano built rear derailleur is much better and more durable than the Allvit. The model J freewheel is better and more durable too, but the model F is a good one so it doesn't matter all that much EXCEPT for the more useful hill climbing of the model J. The 1967 model is the first COLLEGIATE to have the great (s) Schwinn stik stem shifter. 1966 model has the excellent, stronger thicker headtube frame.... 1974 through 1977 Collegiate have the GT-120 (shimano) rear derailleur which looks more like a typical Lark/Skylark/Eagle unit, as the high and low limit adjustment screws are in the more familiar location than the earlier GT-100 which schwinn engineering had shimano build with adjustment locations different than the typical Lark.... The Suburban five speed (introduced into Schwinn line-up for 1970 model year) also featured the same shimano built rear derailleurs and the exact same model J 32-14 freewheel and 46 teeth front pedal crankwheel as the 1970 and later Collegiates. Earlier Collegiates also had the 46 teeth front crankwheel.........just with the model F 28-14 freewheel gearing and an Allvit made by Huret.
Don't sell those ancient Collegiates and five speed Suburbans short. They are great, smooth riding bicycles that are among the most durable geared bicycles ever built. Yes, they are heavy but they are great bicycles for slow riding and the 1970 and later models have almost the same gear range as most ten speeds. The 32 tooth first gear of the 1970 and later models will allow you to climb most any hill even as heavy as those electro-forged schwinns are. Another thing that is worth mentioning is that the factory seats of say the 1971 and later Collegiates/Suburbans are much much more comfortable than all those S colorful two tone deluxe and black springed seats of 1969. You can find much info as to the paint colors and the frame sizes offered year by year..............GOOGLE 1971 Schwinn Catalog , and you'll find waterford's link where they host the 1971-1980 catalogs............if you GOOGLE 1969 Schwinn Catalog.........or 1970.....or 196x whatever.....you should find waterford's link for 1961-1970 catalogs.................then just spend some time scrolling through... There is also another site that hosts something that they themselves compiled called the Lightweight Schwinn Data Book, or something very similarly worded........google that and you should see three distinct volumes or perhaps it is four volumes that each cover about a five year period....
Now there is another alternative in your quest............this is a current, cheap but simple 7 speed bicycle that PACIFIC CYCLE manufactures in China which has a mixte frame but there is ONLY one frame size.......it comes in three different colors that I know of...........The "BUTTER" color which is a sort of yellowed-off white is the best looking of the choices available today.................there is an aqua-seagreen color that looks like the Miami Dolphins team color......... PACIFIC CYCLE badges this made in china 7 speed as the Schwinn Admiral. It is not too bad if assembled properly and lubricated. They likely do not come with sufficient greasing of the bearings if you get it from the floor shelves at Walmart, Target, or one of those major sporting goods box stores. Walmart has sometimes been out-of-stock with these on their website but recently was back in stock........there are many resellers who resell these new bikes on ebay and elsewhere online for two times the price, just as they did when Walmart had the new $125 Stingray copies a couple of months ago.........people immediately bought them for resale on ebay for Xmas season at prices above $400.
Pacific Cycle has had models by the names of GATEWAY and WAYFARER and something else I cannot recall which are similar cheapie 7 speed bikes with step through women's or men's frame.............again there is only one size frame............handlebars differ some according to model name................all of these cheapie Pacific Cycle offerings of the past five to seven years have decent aluminum 700C wheels with tire width of approx 37mm or there abouts.....so hybrid style.................. The steel chromed handlebars and fenders that these Chinese made cheapies have will rust and degrade quickly if not stored indoors or exposed to rain/humidity/water. They aren't all that bad, the paintwork is good, the welds are strong enough even if they look like an idiot welded the frames.....the wheels are decent quaility....the bike is simple enough...........yes, the twist shifters are somewhat fragile, as is the rear derailleur, but inexpensive enough to replace when they do break......the quality of the metal teeth on the rear wheel gears is minimally acceptable at best but it does function......... the pedals are plastic crap and should be replaced immediately with new old fashioned repoduction $15 replacement pedals........................other than that, those Pacific Cycle cheapies from China actually ride decent if the person riding it fits the one size frame......seat adjustment and minimal bar adjustment...................if you're gonna ride on of these Pacific Cycle cheapies, in my opinion you might want to retro fit a used 7881 handlebar from some 1967 to 1977 Chicago Schwinn as it will improve not only looks but rider comfort. That is something that many of the off the shelf cheapie big box beach cruisers and 7 speed hybrids can benefit from. In addition to these new Pacific Cycle cheapies with 37-622mm 700c tires, you'll see some fat tire heavier 7 speed cruiser bikes at Wallyworld and Tar-jay that aren't too bad, certainly not terrible, ....paintwork is nice for cheapie but again other than the wheels, the other gear components and shifters are somewhat fragile, same rust issues.....one piece crank versions are likely more durable.... Don't expect any of these to be as durable as a 1974 Columbia, Ross, Huffy, Murray, FIVE SPEED near clone of the Schwinn Collegiate, was. The modern cheapie chinese bikes have better wheels than the old bikes but durability of everything other than the frame , wheels and shift & brake cables is not as good. The modern cheapie chinese bikes weigh about 4 pounds less. They do ride fine if you're okay with heavy weight and slow riding and you can fit these one size offering bicycles. You may want to go with an ancient bike for size offerings and perhaps better durability if bicycle is in very good condition and freshly serviced. Paying inflated prices far and above the typical under $160 in store and web prices that these new cheapies were priced at in Spring of 2019 may not be thing to do, now that some of these same new bikes are sometimes selling for near $300 or more. Still, given the Pandemic situation and the demand for bicycles as a way to have family fun........................there is no reason not to do whatever is reasonable to enjoy riding now......................................who cares if you pay more than it's worth for a used bike, or for that new cheapie Wallyworld type bike.......
The enjoyment that you get now may just be the Rx for reducing stress and having fun family time during this crazy pandemic. You just might not be able to immediately find what you really would like to, but you should be able to locate something within two weeks or a possibly a month that will let you have bicycle fun with your family. You certainly won't look back twenty years from now and think oh how I overpayed for that crummy bike from Wallyworld (or ebay, Craigs, Amazon, etc..). What you will remember is the good-times that you had riding with your family members, having a ball, when the extraordinary time of the Pandemic did not allow for many recreational activities and entertainment options due to the need to social distance. Have fun within what Fauci would consider acceptable, so don't worry so much about the perfect bike.............just get something that works for you........................you can always get something better when you can find it..........It is February and there are only about 30 days left of Winter no matter what the rodent Puxatawny Phil says. Don't let potential good times pass you by because you're waiting on the great bike............... Two wheels, roadworthy and you can comfortably fit, will be okay until then. Just remember to wear a helmet and maintain a minimum of six feet social distancing, and carry your mask along with you in your pocket or bag if you find yourself in a situation where it might be prudent.