Heart of stone

Sixteen year old Cressida Lovelock's life is turned upside down in a matter of hours when her whole family dies in a car accident. When she awakens, two strangers called Percy and Annabeth tell her all the stories her stepfather was talking about are true, and that she is a daughter of Poseidon. Though she has no idea why, she is at a place called Camp Half-blood. Cressida will have to chose between who she is, and who she pretends to be.