From these rules, she concludes that the best thing she can do is cut herself off from others. So, her mother's idea that she should spend the summer at a "grief camp" with other children who are dealing with a recent loss seems the last thing she wants to be doing. But her mother is insistent and Lila finally agrees to go for a single week.
Once there, it is everything she feared it would be and she hates it, but in the end she stays the entire eight weeks. And in that period, she gradually opens up again and begins to re-learn how to trust and develop close relationships. She also works through her anger at her father and understand what drove him to end his life, achieving peace with his decision.
While the story is largely predictable in its outcome, it does an excellent job with the material. Lila's path to healing is very much intertwined with the relationships she develops at camp (and at some distance with her mother back home as well). The author does an excellent job of building that journey in a gradual and believable fashion allowing us to follow along and understand the process organically. Some of Lila's discoveries are from discoveries she makes about her father's background (learning to understand how her father could both love her and still end his life), but many more of them come from learning about her fellow campers. A relationship with a boy with an entirely different sort of loss helps to illuminate that not all grief comes from death.
Overall, a familiar topic, but dealt with in an original enough way to make it interesting and enlightening.