Epigraphs are like little appetizers to the great entrée of a story. They illuminate important aspects of the story, and they get us headed in the right direction.
"The best way out is always through."—Robert Frost
What's up with the epigraph?
The epigraph refers to Annabel's overall fondness for avoidance. She doesn't want to face her problems or hurt anyone's feelings, so instead she avoids the big issues in her life and hopes that they'll go away. But that's no way to resolve your issues, as Annabel soon finds out. She can't wish away the fact that her rape happened, and she can't pretend that her family doesn't have its own problems.
In fact the only way that anyone in the book starts to heal at all is by working through the bad things that have happened. It's only when Annabel starts to open up about what happened to her that she begins to comes to terms with being assaulted—she has to work through it in order to come out better at the end.