I need help with this b*tch in my school...?

Okay, so, I'm 13, and this girl is 14. She rides my bus, & she's about 7 inches taller than me, & she talks alot of **** about me. One thing that pissed me off more than anything, was there was a picture of me and these girls on Facebook, and she felt the need to comment and be like "Wow! you guys are all gorgeous...except Emily..." & thats me. So, anyway, she always wants to talk all this **** about me, yet she wont say anything to me face. We've had history and she wanted to fight me, but she was gonna bring people and I'm not down with that. So what should I do? & some things about her, shes more masculine than feminine, shes a slut & shes already slept with someone and she's in the 8th grade (i'm in 7th), shes like, in all honesty (and not because i hate the skank) like, the ugliest person i've ever seen..she looks like a witch. So, anything I can say to back her down and stop talking sh*t about me? Thanks (: