Teenage girls can be pretty fucking evil. I should know. I was one. One day, school is this fun place where everyone is nice and gets along, and then one day suddenly vicious wolves.
Seriously, teenage girls get away with way too much bullying in society because we have a view that "oh, they're just girls, they can't hurt you" or "sticks and stones may break your bones but words will never hurt you" or "well, if they're treating you like this, you must be weird and you must have done something to deserve it."
Yeah, but it this way, I'm glad my high school years are well and truly behind me.