Anderson writes teen novels on intense subjects that need to be addressed. Wintergirls tells the story of Lia's life after her best friend Cassie passes away alone in a motel room. Lia and Cassie had been friends since childhood and they made a pact with each other to be the skinniest girls in school. After years of starving, cutting and hospitalizations, Lia still doesn't give up o her quest to be skinny. She learns ways to hide her real weight from her divorced parents. Her mother is a doctor that always tried to "fix" her so Lia ended up moving in with her father and his new family. Lia loves her stepsister Emma and often tries to cheer her up when her mom is getting on her case. As Lia unfolds the mystery of what exactly happened to Cassie from the time they stopped speaking six months ago until her death, she sheds pound by pound without anyone noticing.
Anderson really captures what the mindset of an anorexic teenager must be like. She portrays a teenager in a vivid way that almost makes the reader forget that the author herself isn't one. Lia's family situation is complicated and without Cassie she doesn't have anyone who understands her and her obsessive need to be thin. Anderson portrays this emotion realistically but also intertwines it with rich and slightly disturbing imagery. She uses the sense of coldness that Lia feels to really define the title of the novel. Lia has spent so much of her time becoming a Wintergirl that she doesn't know how to get back to the surface and start living her life without Cassie and their pact.