If I were you, I would just cut it off,

I'm not saying that you should stop talking to her, but show her that you have interest in other women, From what I've seen in life, Girls in highschool get mega attracted to guys that can move on and show that they don't have to mourn over one chick.

so talk to other people, and if she starts acting weird because your not showing her the special type of attention anymore, then you know she has some type of feelings for you, and if she doesn't, then you know there is really nothing there, and maybe staying friends is the best option.