Wintergirls by Laurie Halse Anderson is about what it's like to struggle with self-harm and eating disorders, especially through incredibly difficult life events. Because of Lia's difficulties combating the emotional trauma that she suffered because of her friend Cassie's death, Lia sinks into a deep hole of depression and copes by self-harming and by working even harder to reduce her eating and increase her exercise. During this spiral, Lia repeatedly imagines Cassie's ghost encouraging her to die.
After a near-death experience, complete with Cassie's continued pleas for Lia to join her in death, Lia decides to divert from the destructive path she has been on, choosing to live instead. After making this important first step, Lia chooses to voluntarily enroll herself in a psychiatric hospital. Another important way that Lia combats her negative emotions is recognizing and choosing to believe that her friendship with Cassie was toxic. Lia comes to understand this because of how Cassie's ghost treats her; Lia doesn't value friends who want her to die.
While Lia knows that her treatment will be a difficult process and that she might slide back into these unhealthy coping mechanisms in the future, she is committed to maintaining the love for herself that she gained through these grueling experiences.