From my experience in high school here is a general advice:
Just take it easy and stop getting so worked up about everything. People always try to make their life like soap operas, but they're not, relax.
As for the girl, it seems to me that if she's just spreading rumors and shit about you for no genuine reason then just stop helping her out. Still talk to her and stuff, but don't give her the time of day if she doesn't show you the respect you seem to deserve. If she apologizes then it's a different situation, but from my point of view she definitely seems very immature and immature people will only bring you trouble.
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