Start with Barbara Leckie, Girls Bullying behaviours and Peer Relationships. The Double edged sword of Exclusion.
If you have access to CINAHL there is a huge amount of research into what is labeled "Horizontal Violence in Nursing"
"The Mean Girls of ER" Marie Claire Magazine.
In the Company of Women: Indirect Aggression Among Women: Why We Hurt Each Other and How to Stop [Heim, Pat, Murphy, Susan, Golant, Susan K.] on amazon.com.
There are also some YouTube videos on the subject including this one.