My so called friend?

I have a friend who ive been going around with for yrs. My family has always been nice to her and she used to come ova my house and we gab her food evryday. she was practically livin there. She betrayed my sister once n took sides w. my sisters enemies n left my sister to deal with no friends in hs. So my sister moved to Texas where she suffered miserably with my aunt. She came back though and we all became friends again. Later she made enemies with my sisters new friends n so my sister thought it would be nice to take revenge n took their sides. The same thing she did to her.I took her side. Dats y i transferred out of 1 of the best hs in ny n moved 2 a local skool because 1/2 of her enemies went there n I couldnt deal w. them. In the new school she made enemies n I took sides w.her once again. We used 2 not go to skool. All of a suddn she says I wnt 2 g2 skool n not b friends w. u no more. I dnt g2 skool. She dunt c her enemies. but i do so i dont go. I want revenge. What shuld I do