Who is Darleen from King of the Screwups and what is their importance?

Darleen lives in the trailer next door to Pete. She is described as studious and artistic. Darleen lives with alone her father, as her mother left them a few years prior. She stages protests and boycotts at school, and most of the kids think she is a pain. Over the course of the novel, Darlene and Liam become friends.