My Secret Bully by Trudy Ludwig (2015)
Here is the all-too-familiar story of Monica. She and Katie have been friends since kindergarten. Monica loves being around her when she's nice. But there are times when Katie can be just plain mean. And Monica doesn't understand why. Monica is a target of relational aggression, emotional bullying among friends who will use name-calling and manipulation to humiliate and exclude. But with a little help from a supportive adult—her mother—Monica learns to cope and thrive by facing her fears and reclaiming power from her bully.