Sounds like the exact situation that my fiancee/wife/s.o. is in. Fits all kids gear. She gets top of the line gear for cheap because it is youth sizes. When I first met her I wondered how she could afford all of this top of the line gear and then she let me in on the secret of fitting youth sizes.
Anyway, bikes can be modified to what you need. Seats can be shaved, suspension and parts can be adjusted up and down, etc... When I first met my other half, she was man handling a 2001 CBR 929, just had a little trouble flat footing it, and a CBR F2. She is 5'2"not sure of weight because women never tell the truth about it, but small frame fits the bill. I must say the F2 fit her really really well. She could touch no matter what the terrain.
Go sit on bikes that you like. Find something that has a slim and narrow seat. Wider the seat, the less footing you will have. Just make sure it is a machine that is not over your riding experience, you can handle well, but also grow into so that you don't feel bored and have the need to jump to something big in a short period of time.