Have you thought about allowing her to go naked from the waist down, or wear a dress without undies on? Eventhough undies don't feel exactly like a diaper, it is still something against her skin assimilating a diaper. There may be a few accidents on the floor at first, but if you redirect her to the potty as quickly as you can (mid-accident if you can), then if she is ready, she will catch on quickly. If you have a full weekend (or two or three days while your son is at school) that you can devote to working with her on this and spending as much time with and/or near her as possible to redirect accidents, you should be able to tell if she is ready.
It took my son about a week before he was ready to be in underwear full time, but then he was in it night and day. He has only had about 3 or 4 nighttime accidents (and they were usually in the morning because we didn't make it to the bathroom in time), and only has accidents at daycare (I think he gets too busy to stop sometimes?). Though for the last 3 weeks he has been accident-free!
As hard as it is, treat accidents as non-chalantly as you can. She is NOT doing this on purpose, and getting angry with her could create an aversion to potty learning (because she is actually learning something -- just like colors, numbers, etc.) as a whole. Just something like "Pee/poop goes in the potty. Next time you need to go, let me know, and I will help." If after 3 or 4 days, she doesn't seem to be getting it. Stop for a week or two, and then try again.
I agree with pp -- try to relax. She will not go to college in diapers. It will happen in time and ONLY when she is ready. This isn't something you can force -- only gently guide. If she is resistant, there won't be much you can do but to give it time.
I didn't use rewards with the exception of praise, celebration, dancing, etc. Micah was just shy of 25 months when he was in full time undies.