if you like someone and you don't know how to tell her because she likes someone else what do you do?

Answer 1

well that depends..do you know her well? is she a friend of yours? is she hooked up with the guy she likes?
well, if she isnt a friend, you should be friends with her, get to know her
if she is a friend, just remain friends...for now
if she has a broken heart, good friends like you (i hope) will help her out
be patient... if you are meant to be, it will come

Answer 2

I'm going to say stiff upper lip. Not much you can do. If she knows you, and who you are, and doesn't like you like that then there's not much you can do. Just stay within firing range. She may change her mind in time.