I'd guess easily 25lb but don't be surprised by closer to 30, picked up a pair of trek 220s from craigslist, one from 1999 the other 2001 and they both tip the scales at just over 30lb. Steel stem, handlebars, seatpost and cheap hubs all drive up the weight. The C-dale that just replaced them is 4lb less with disc brakes and a suspension fork. I'll be changing out the kenda small block 8 for rocket rons and the basic fork for a spinner air shock which should shave off 2more lb. Kid's bikes are really just heavy, no way around it without spending a lot.
Replace the brake pads and the grips, both will be old hardened rubber and the bike will stop faster and feel better with new. Other then that as was mentioned regrease the bearings in the headset, hubs and bb and just have her ride it.