Lovely school friendship problem to solve...?

Don't change who u r 2 fit n,u mite have 2 pull her aside and tell her about herself,that way she can't say u confronted her while u were hanging out with either of the groups,that way your being honest,and up front and she can except what u said,and better her attitude,or pick a group and stay n it.and if that doesn't work,when she's hangin out with 1 group speak 2 every1 else,excuse yoself from that group,and go 2 the other 1,and when your friends ask y u left tell them because u cant deal wit ms.nagativety.and leave it at that.