My cousin is a brat!!please help me!?

I don't know what to do, my cousin has no respect for anyone! She thinks she can do and get whatever she wants! Shes cusses a lot right in front of all the adults and all her mom says is "BECCA" she does not get on to her at all neither does her dad...she called me an a** face, and she called my 2 year old cousin a p***y. She thinks shes so much better than everyone else, today she said i bet you beg your friends for a boyfriend (after i told her that i don't care about the superficial things in life.) I can't deal with it anymore i cant stand people like that.Its been five years since ive seen my grandparents and aunts, uncles and other cousins, and when i said to her you have it good here, she gave a smart alecy smirk and said i know (trying to be cute.) I know this is bad but when she is like this i just want to smack her upside the head. She just gets on my nerves i don't know what to do anymore. Right now I'm at the point where i might lose it! Ive lost all respect for her. Please help i don't know what to do anymore!!! And if your going to be rude to me, i don't need it.Thanks. Shes 11 if that helps.