Dess and Hope (Peas and Carrots, by Tanita S. Davis)Read about the other entries on the list.
Dess just wants to be reunited with her baby brother, but that means going to live with his foster family, since they haven’t seen their biological mother in years. And when Dess arrives, she finds she has a foster sister just her age, Hope. They are instant enemies. Hope sees Dess as rude, and she doesn’t like that Dess already seems to be fitting in with the cooler kids at school. But being forced to live together helps them to start seeing the ways they can help each other.