>>1 There's multiple ways you can take on this situation.
First, do you know her well? If not, try talking to her more often. Ask her what she likes, what she doesn't like, things of the such. Then, once you get to know her well enough, ask her out.
Or, you could just ask her out right now. But given what you have said, it seems she is either oblivious to your feelings, is ignoring them, or knows that you like her but is not sure what to do.
If she really didn't notice you after all these years, and you already tried getting to know her, just ask her out already. If she says no, just move on.
Good luck