Rlyss

Sorry I don't have time for a super long response but I don't even think this needs one.

This girl is just a silly high school girl that doesn't know what she wants. Forget about her, be cool with the rest of your friends, don't spread rumors about her or force them to side with her. Just be cool with your friends, ignore the shit she does and everyone else will too. She's acting silly because she's nervous and doesn't know how to respond to all this in a more mature way.

Whether she's not showing her true colors or not doesn't matter. Move on, live a crazy high school life and meet lots of people, stick with your friends and they'll put her in her place if they can see she's acting stupid.

Edit: Just to be a bit more specific, don't tell her you don't like her anymore, don't tell her you never did, don't tell her you don't want to be friends. Don't do anything like that. If she asks you just say that everything's cool now and that you can see it wouldn't work out, keep her in the group because they're her friends too, and I bet she'll chill out soon enough.