Her Evil Twin is the sixth book in the Poison Apple franchise. It is written by Mimi McCoy.
Anna's new friend Emma is fearless, fashionable, and always up for a new adventure. But Emma is also a troublemaker. She sneaks off school playgrounds at lunch and borrows spray paint from the art classroom. Emma never seems to get caught, but Anna does. After all, the girls look so much alike—who could tell them apart? But when Emma's idea of fun takes a sinister turn, Anna starts to worry about her friend who is in danger! Should Anna be Emma's friend or should she be her school mates friend? Is her new BFF actually her dangerous evil twin?