I so agree with the PP who said kids need to be allowed to vent like adults do but just have to be taught how to do it. How many of us vent about someone to our DH, friend, or online. Hell, look at this website (although mostly the general one) to see how people vent, make fun of, bitch about each other.
I bullied one kid, once. It was only once because I got caught, received detention, and had to write the girl a letter apologizing. I felt horrible and never did it again. But I bullied that girl because I was being bullied, and in my 11 year old head, picking on someone else made me feel better. So I agree just talk to her about bullying in general and ask how things are going at school. You might be shocked to find out that she's not the bully, but the one being bullied.