I agree with the above about position. My girlfriend is 5'5" and I had a hard time finding a bike to fit her and she can't comfortably stand over her 52cm frame but she WANTED to ride and is now very comfortable on her bike. I explained to her that she shouldn't be able to put her feet on the ground and she got used to it. If your GF is too scared to really go for it maybe cycling isn't for her?