I need advice........?

Tell her that you're annoyed that she's always insulting you. Tell her that it's not only annoying but it hurts your feelings. If she says sorry but continues to do it, tell your girlfriend (her best friend) to talk to her about it instead. If she still won't stop, then don't be friends with her anymore. You can still joke around, be nice to her but don't be her friend anymore. Whatever happens, at least you know that you tried to be friends with her.