Unfortunately you can't change how people feel. It's one of the hardest things to deal with in life... especially when it comes to love.
I think if she's not interested in you, there's really nothing you can do.
Based on my experience, my advice would be to stay completely away from her and your friend for awhile. Give yourself some time to get over what has happened. And please, don't worry! You're young, and you'll eventually find a girl more stellar than this one!