Oh Celp, I so, so feel your pain, confusion and anguish! This happened to my daughter at about 11 / 12 years old. She had been "best friends" with a little girl all through primary school, and they did everything together, literally, everything, always. At the time of moving up to the comprehensive, my daughter went through puberty a little later than her peers, and her "best friend" and she developed spots, gained weight, and was not the pretty little fairy she used to be. Things went wrong at senior school, and she often came home in tears... and it transpired her "best friend" had told her that now she had met some new, really pretty girls, and that she was no longer one of the "pretty set" so had to be excluded. This time was utterly dreadful for us all, and eventually she made some new friends (who are now, and still some 20 years later, very close and successful, and adorable.) My daughter still remembers this, as tho it happened "yesterday", but insists that it taught her one of her lifes' most important lessons. She is now a very successful (incredibly beautiful) slim and vivacious young lady, with an adoring partner and a fantastic job, earning buckets. But have to tell you this, and please don't hate me... but that little madam "best friend" started to become really rather ugly as a 15 year-old ... as she grew into her body - she piled on weight, as my daughter simultaneously lost it, she developed acne, and her "pretty set" friends dropped her. She is now a shop assistant in a bargain shop, and has two children from two broken relationships. My advice is to help/allow your daughter to drop this girl who is NOT a friend at all, and get out there and get your daughter involved in all sorts of exciting activities, and "different" experiences and widen her horizon. Don't even "try" to work with, or discuss with the other parents. You will be on a hiding to nothing, ... remember, their parenting "produced" this childs' behaviour! 13 is such a desperately delicate age. Engulf her in family fun, love and delight and to HELL with the non-friend little no-bodies who are not friends at all. It is hard, but she is worth so much more! Good luck. xxxxxxxxxxxxxxxxxxxxx