What should i do?!! im in 6th gr btw. and theres this girl who hates me but acts like she likes me!! idg it!?

there's this girl at my school named sam. she's really and funny nice to everyone. at school she's all like "hi!!" and "i love you" and "u rock", but actually, when she's not trying to be all nice, she talks about me behind my back ALL the time. i used to hang out with her and her friends in the beginning of the year, but then i left them for TRUE friends when they all started being mean to me (except 4 people- carly, dana, erin, and cat, who r nice 2 me). and i dont even hang out with sam, and she still gossips about me. like she started so many rumors about me, and talks about me and laughs at me behind my back. i know she hates me. and i know she does all this because carly and dana told me. but i dont understand this: why does sam act like she loves me and tries to act super nice to me, when she really hates me? and she tries to be nice to everyone, because she doesnt want people to hate her im guessing. but she said she hates so many people (she has a "hate list"). wat should i do