What do i do about THis annoying girl?

my friends have been in this group for like 4 years and this is the first time we have ever had drama! this girl (She and I were the first two people in the group) strated being VERRY mean and acting like a preppy (that what my friends call the mean girls who are super rude and only care about how straight their hair is and not their grades oh and btw ARE MEAN TO EVERYONE!) and so we confronted her and then she got allumm... err... "female doggy" on us and then tried to go sit with the preppys but she got rejected and started hanging out with the only girl in the group who likes us. then she started sending us personal text messages. like she told my friend that the only thing yu need to thrive in this world is talent, looks, and popularity, then she said, which is why i will thrive unlike you. And she kept sending texts like those and being really mean on facebook. WE HAVE TRIED THE WHOLE YEAR TO GET RID OF HER! So we decided the only reason she still hangs with us is because my friend (lets call her amanda) keeps inviting her. so we confronted amanda and asked her to either tell her to leave or leave hersself because we were sick of being bulied and then amanda went home and nearly switched schools! we went to the office about it and then the mean girl accted all innocent and said we were lying! WHAT DO WE DO!?!