My best friend is a nasty person?

Ok so my best friend always talks behind peoples backs to me and it's always something mean!! I try not to get caught up in gossiping but it's so hard not to!! I don't want to be a bad person like that. She doesnt have any friends but me and I kinda feel bad 4 her. That's y I am still her friend. I have lots of friends but no bffs Like her. Like a bff that u can talk about ur crush with and tell ur most emberessing secretes to. She hasn't spilled any of my secrets so she's good in that way. But she always calls me a dork or stupid or a fail and it hurts me. I don't want to just ditch her because then she would have NOBODY and that's very bad. Ahhhhh idk what to do. Were in a fight right now because she purposely poured paint all over my nice white blouse just because I jokingly called her weird.( In.Nice way) :( what would u do? Should I stop being her friend or keep being friends with her?? Thank u