First, I would make sure she has some romantic feelings toward you before you go and try to get her committed to you. Ask her out on a few dates before you go asking her to be your girlfriend. If you don't know if she has feelings toward you, she probably doesn't and you may be setting yourself up for a big letdown. That should be something easily recognizable. If you know that she does, it should be as easy as taking her out to dinner and asking her. No risk, no reward.