Girl bullying is often called "relational aggression". Much information can be found online, including The Ophelia Project. The book "Queen Bees and Wannabes" (3rd edition, July 2016) may also be of interest.

If you are concerned that your daughter changing classrooms may be interpreted by some that she has been a bully, these are my tips:
1) She needs to ensure that what she says and what she does do not resemble bullying. For example, when disagreeing, she must focus on the issue and sources which inform different positions or viewpoints, and must NOT make personal statements about any individual (ad hominem attacks).
2) She (and her parents) must simply dismiss any inquiries about the classroom change as "being a better fit." (Similar to ElizabethN's post above, which gives great advice, IMO.)
3) If others make conjecture, rumors, or negative statements, both daughter and parents must take the high road by simply stating that it appears some others others may be making conjecture and you will not engage in that.
4) No gossip, no bashing others to prove your daughter or yourself "right".
5) Let it go.
6) Move forward.
smile