How Many Letters Are In Goodbye?

It's been almost eleven years since Rhea Farrell last wrote to her mother. It was a Friday night ritual - until Rhea's father decided it was stupid to write letters to a dead person. That was the summer before the accident. The summer before Rhea began to keep her first secret. Now about to turn eighteen, far from home and alone on the streets of New York, Rhea finds herself the holder of many more secrets.
So, just like she used to do as a little girl, she begins a letter with the words 'Dear Mum' and tells her mother the things she can't tell anyone else. But is it enough, to confide in someone who can never answer? Or is it the only way she knows how to say goodbye?