Davis, I won't say I'm older and wiser, but I will say I'm older and have been there. You have two things going for you: 1. She knows your name. She has taken the time to get to know something about you. Unless she has a photographic memory or you are a celebrity, this took a little effort on her part. 2. You have already had a conversation with her, so it would not be totally out of the blue. You should ask her out. If she rejects you, you feel bad for a little bit, but she goes away to college and you don't have to see her anymore. Even if she tells the school what a geek you are, the embarrasment will go away in a few days. Regret can stay with you for a lifetime. Imagine 10-15 years down the line. You are still single and wondering what could have been or you are married and maybe the marriage doesn't have the same fire it once did and you are still wondering about this girl you knew in high school. Regret is a powerful thing.
Also, someone mentioned about when she goes off to college. Yes, that may present a problem, but she could go and see all the guys at college are jerks compared to you. If you ask her out, you can get her phone number and you can find out where she will be staying at college. You can call her or send her a letter every few weeks just to let her know you are thinking of her and that makes her think of you and what a nice and thoughtful guy you are. Some long distance relationships work. Her being two years older may seem like a big deal in high school and college, but it is not a big deal in the real world.