How to Get Rid of My Best Freind in Ten Days?

I have this friend who is so jealous from me when i talk to guys. i some times feel that she is taking my happiness but when i leave her and tell her i don't want to be her friend ,she keeps telling false stories about me to the class and everyone beleives her. she tells them that i left her for no reason but i do have reason for that and i told her and her grandmother is a bitch!. Her grandmother once called me , telling me that i shouldn't hangout with girls who are older than me (just becase i hangout with dana who is older than me and her grand daughter hangs out with her too) because dana talks about guys and talks with them
and here where i live in it's strict for a girl to talk to a guy( i don't see why, for me, it's normal. I not actually local where i live in). And, anyway, It's non of the old lady's bussiness of whom i hang out with or talk to whom. she should tell taht to her grand-daughter, NOT ME!.

Anybody got any advice, how can i get rid of her by not not getting blamed from my class?

By the way i didn't tell you that my best friend is a coward.