What should i do about this girl?

Ok so this girl sarah is such a slut. She is in 6th grade and flirts with this 8th grader on the bus all the time. He doesnt like her and hes told her that. She HAD a boyfriend untill i told him about this. He dumped her. Anyways she like takes her shirt off on the bus and has a low cut cami on underneeth that shows half her bra. And she keeps talking to me and i HATE her. How do i get her to know i hate her???! I wanna be mean Oh and shes emo too.