How does Izzy grow and change over the course of the novel, What She Left Behind?

Izzy has a stack of unopened letters her incarcerated mother has sent her over the years that Izzy has never read. They tell the true story of how and why Izzy's mother came to shoot Izzy's father to death. They symbolically act to remind the reader of the irony that while Izzy has the courage to read the private journal of Clara and fully investigate Clara's life, Izzy lacks the confidence to apply the same detective skills to her own mother. Only when Izzy loses her mother to death can Izzy bring herself to finally confront the truth of what is contained in the letters. So in this sense, the letters also act as a marker to show how much Izzy has matured as the story progresses.