Nawww, Height don't matter! I mean- my bf is 6'2 and i'm 5'2. =)
Tbh, the same thing happened to me in middle school. I had a crush and i knew the dude didn't like me back but i stayed around him and talked to him a lot. (Maybe try to get her number?) After a month passed he asked me out FINALLY! ;)
*Tell her how you feel about her.*
^^^ That's the best thing to do. Hope this helps! =) Gl in life!!