This girl at shool is MEAN! she wants to fight me. And turn ppl against me!! Help!?

So my ex friend suddenly turned against me. Just cuz j wanted talk to my bff about my grandpa passing away.. So she saw us talkig and said that we were laughing and talking to other ppl.. And then she is also mad at me and my bff cuz her ex bf told us somethig bout him that we cant tell her. So she pushed me. Twice. She threatened to punch me in the face.. Im not scared of her at all.. I do a bunch of martial arts an im pretty sure i can beat her upp.. And she wants to fight me. I told her that shes a piece of trash. And i told ber im not sinking tk her low lvl. But shes always coming upto us and cussing. Shez trying to turn ppl against us and shes a big brat. I hate her... I dunno wt to do. Wt should i tell her the nxt time she comes up to us??? Plz help!!