Who is Callie Vernon from The It Girl and what is their importance?

Callie Vernon is the beautiful roommate of Jenny Humphrey and Brett Messerschmidt. She is a junior at Waverly Academy and plays field hockey. Callie is dating Easy Walsh, and she is manipulative and controlling. She has the suspicion that her previous roommate, Tinsley, was expelled because she was sold out by Brett. But without evidence to go on, Callie does not say anything.