Hi
Belmont Wheelworks probably has the largest selection in Boston including Raleigh which are cheap and easy to ride. They also have a repair guy but they're a bit selective in which bikes they will work on.... . Try not to go there on a weekend, if possible! It's super busy then, and they are crusty to start with and on the weekends, they can get a bit gruff. 'Nuff said. Ebikes of new England in Derry NH and goodales also in NH would be good places to try, esp ebikes of NewEngland, which has a wide selection. There's a Haibike dealer in Brockton, and I found a Haibike hard 4 for $1799 on line last night at ebikes508 in Brockton.(UPDATE-- that bike seems to be gone.....
)Also one for $999 at eboomelectricbikes but I wonder if it's really in stock... That is the only bike I know of designed for smaller people. Good luck and let me know what you find!
I had another thought - if she already has a bike which fits, you could put a kit on it - for example, ebikekit has a 16", 20" and 24" inch option for both front and rear wheels. I have an early (2012) kit which has tremendous power and will get me up to 25 MPH, and they have now added a PAS sensor to the kit. It only took me a few hours to put it together as a complete newbie (minus the PAS which was not available then). These are powerful motors but I think you can set it so that it doesn't exceed a certain speed. the Ebike kit people will happily assist you in deciding about this. Lunacycle is another place for a kit and they get excellent reviews. I'm sure there's a kit section of this forum with tons of other suggestions.
all best wishes,
Susie