Worse Than Boys by Catherine MacPhail.
I finished reading this book last week, and it is a very good book.
It is about a girl called Hannah Driscoll, who is in with a group of girls who have been tagged The Lip Gloss Girls. Her friends in The Lip Gloss Girls are Erin, Heather and Rose.
They are in a serious rivalry with another gang of girls, the Hellcats; Wizzie, Lauren, Grace and Sonya. They fight so much they have even been called "Worse than boys", as they're fighting is so serious.
Hannah and Erin are the best of friends, until one day Hannah's world comes crashing down.
The Lip Gloss Girls are convinced Hannah has disowned them, and block her out of they're world and everyone else's in the process, no matter what Hannah does to object, they don't believe her.
Soon, Hannah becomes depressed and upset, crying herself sick when she gets home from school, crying herself to sleep every night.
She is pretty much the laughing stock of the school, as she now has no friends as everyone thinks she will disown them as she apparently did the Lip Gloss Girls.
But what happens to Hannah?
You'll just have to read the book to find out!!