Eleven year old biting

What do you do with 11 year old? That wants to bite other kids.. She was talking to another girl when another girl showed up. And she didn't want that girl there. She put her hands up and then. I guess proceeded to bite the girl. This was at an after school program. What counselor said the girl had a bite mark on her arm. But she tells her Grandma she didn't do it. The counselor told her that this is what happened when her Grandma came to pick her up. Eleven year old girl how insane to bite another person. I am losing hope with her bad behavior.HELP!!!!I will be the call tomorrow