there should be a process of gradually alienating her. You can't just ignore her and stay away from her. In that way, without friendship, we will become enemies. It can't be black or white.
gradually alienate her. Gradually give her less contact. After a long time, she will feel it, and then she will do her own thing.
Of course, you have to continue your investigation. You can't think your classmates are vain at once. When on earth was she vain? Sometimes in order to protect yourself, you may have to be vain. If everything stays vain, you really can't get along with her. Plus, I am a particularly pragmatic person. Isn't that just a contradiction? Life is too awkward? It's really boring. It's better to leave her.
gradually make new friends. There will be new friendships, and friends will be constantly replaced, which does not mean that a friend will always be a friend. Of course, if you have new friends, you'd better not forget your old friends. It's ok to say hello to her if you have anything to do, and continue to maintain friendship. Not too far, not too close.