Odd Girl Out: The Hidden Culture of Aggression in Girls by Rachel Simmons
Just finished reading this truly horrifying book. I did not have a comfortable and un-bullied childhood and youth, but it appears I may have had a walk in the park compared with the shit [some/many/most] girls have to put up with. This book details and explains the alternative aggressions which girls use to hurt and bully each other (or to establish social dominance or "popularity" or whatever), why they're used and why they're effective, and why they usually go undetected by adults (parents, teachers, etc.). It's pretty powerful stuff.
In the last two chapters, Ms. Simmons offers some strategies to combat alternative aggressions and some hopes for the future. However, I'm not at all sure how much I'll be able to help Gavi should she run into and have to cope with this kind of behavior. On the other hand, just being able to see and understand things that were previously hidden or unnoticed may well give us a leg up on not falling prey to them.
I recommend it, even though reading it may be hard on your emotions.