I was in the same situation with my wife. One thing that you should realize is that, not only do you have to worry about the fit, but you have to be sensitive about what TYPE of bike she wants. I bought my wife a used road bike that fit her well. However, she was not happy riding it. The more aggressive positioning of the road bike was uncomfortable for her, and the skinny tires weren't confidence inspiring when going over some rough patches. So, long-story short, I sold that and had her try out a few different bikes. She went with a Specialized Stumpjumper (Women's). I took off the knobbies and put slicks on there. She enjoys riding much more now and she is totally comfortable going over little cracks, down curbs and whatever. Perhaps one day when she gets more comfortable being on the bike, she will want to upgrade to a road bike, but for now, she loves her mountain bike. I am fine with that.