Is it weird that I don't want to be friends with her?

Okay so lately I find myself in a very "junior high" sitatuion. I feel so confused.. it's quite funny actually. There is this girl who went to elementary school with me, she was always the girl that everybody thought was "weird and gross". In 5th grade, she would try to hang around with my friends and they would basically tell her to get lost as nice as they could. In 6th and 7th grade, I would be nice to her and actually talk to her (we had all the same cles). I have ALWAYS been nice to her, now she seems to think this means that I have "been her best friend since 3rd grade". LOOOL. So now I'm in the 12th grade and just came to a new school, where all these kids that I grew up with are. (I went to a private school out of the city for the first 3 years of high school). Anyways, she just kind of recognized me and I had been nice to her on facebook when I was at the private school so this reinforces her "best friends theory". Anyways at first I was fine with her following me around but now it's TOO MUCH. This girl has disclosed her secrets to me- how her parents are first cousins with one another, how she will be marrying her cousin, how she doesn't bathe, how she doesn't comb her hair. I tried to tell her that it's bad hygiene but she got all defensive like "WELL I DON'T SMELL BAD!" and she actually does have B.O. One day I told her I didn't want to hang out with her that day and went with another girl to the mall instead, when I got back, she swore at me and was RAGING with anger. Anyways I thought PHEW finally at least it's over but she called me, literally SIX times that weekend apologizing when I kept saying "LISTEN, I DON'T WANT TO BE YOUR FRIEND. I DON'T WANT TO TALK TO YOU." She was like "we're best friends, these types of things are bound to happen." LOL seriously I don't wanna be a ***** because this chick has enough bullies in her life but HOW DO I GET RID OF HER??? UGH HONESTLY when she comes up to me like ~~SOPHIA~~, I want to gouge my eyes out. HELP MEEEE