Why did Maddie feel guilty of herself?

Maddie felt guilty of herself because she always supported Peggy for making fun of Wanda. Despite belonging to a poor family, she always made fun of Wanda. Later, when she saw the beautiful dresses drawn by Wanda all lined up in the classroom, it made her feel guilty of not having said anything when everybody else was teasing Wanda. She chose her loyalty to Peggy over her sense of right and wrong. She could not sleep that night.