Ask her out before you lose your chance and you both regret it forever.. or at least, you regret it. It is always better to do the thing that you would regret NOT doing, then to never do it at all.
Personal note: there was a guy that I was really into a few years ago, but I was too shy to do anything more than drop (big) hints. Apparently he was into me the whole time too, but never said or did anything about it. There was one perfect chance when he could have done something (I was visiting him in his hometown, Pamplona, during the running of the bulls festival), and he never did it. I had no idea that he liked me back until 2 years later, when I joked around and told him how I used to feel, and he 'fessed up and told me he felt the same... too bad no one had any balls to take action when it would have mattered.
I don't care much now since I am with a wonderful man

, but being shy sure denies you of a lot of life's opportunities. I am glad that ktspktsp had the balls to tell me how he felt--a real man gets over his shyness when it really matters.
