What is the theme in The Great Gilly Hopkins by Katherine Paterson?

Seeing what the world really is around you.

Gilly doesn't see/know this at first. She is a bully. She steals money from Mr.Randolph. She really thinks she cannot become a better person. Gilly is so focused on what she thinks is good, that she won't alow herself to appreciate where she's at, and who her foster homes are. It's like the world around her is black an white!