Letters from my unknown hero

Isabel Castner is a normal 18 year old. She gets good grades, and is very beautiful. But what most people don't know is she has an awful past. When she was 6, her birth mother, Sasha, was killed in a car accident by a drunk driver. Her birth father was the murderer, but was never caught. He remarried a woman named Lilly. But even she doesn't know what he did to Sasha. He has kept it from her all these years and abuses his only daughter. When Isabel is a horrible accident like her mother, she survives, but doesn't remember some things. Every Saturday she receives a letter from an unknown person, her hero from the accident. She is now determined to find her hero, and get out of her house, when her father blames her for this crash too. Will she find him/her? and will she be able to escape her "home"?