How do I deal with a bratty seven year old cousin?

She is really annoying! She always hits me when she sees me and then she goes tell her mother that I hit her (NOT true) I mean, I'm almost 14! I'm not gonna go around hitting people half my age! And everytime she comes to my house she messes my whole room up and if I tell her not to she tells her mother I'm being mean or that I hit her. The other problem is that her mother thinks that the girl is an angel and that she's telling the truth!!! WHAT CAN I DO???