I was friends with my current boyfriend for 3-4 before we got together. I've now been with him 4 years this year and it's going great. So that proves it can work out
However, ours went a little differently to yours... I'd
always liked him, from the moment I met him. He started liking me in a... "sexual" way in sixth form... and he asked me out
So you never know, she could have liked you forever and you just don't know it. Tell her you like her! What you got to lose? If you're as close friends as you say you are she won't let it ruin your relationship if she doesn't feel the same way.x Goodluck x.