Is she a frenemy or not?

Frenemy is a good word for it. I say try to give her a reality check, yeah it may hurt her, but she will eventually come to her senses on how much of a good friend you are to her to even tell her. People change over highschool. And if you feel like you should let go her, you should, if she even cares about your friendship, she'll be coming back to you with an apology.