My 5'1" wife now rides a 47cm 5200 Trek with 650mm wheels. It fits her much better than her previous bike which was a 50cm with 700 wheels. The better fit has given her more confidence and she is more comfortable on longer rides. As others have pointed out, with frames this small you need 650 wheels to have reasonable geometry, and the shorter top tube makes more sense for most women having proportionately longer legs and shorter torso.

Al