Black Heart Blue by Louisa Reid

Hephzi stands in her sister Rebecca's dress at her grave, struggling with the loss of a beloved sister and the secrets dammed up inside of her. Hephiz and Rebecca were twins but different in so many ways, Rebecca beautiful and sunny, Rebecca's face twisted by a genetic disorder. Home schooled until Rebecca persuades her parents to let them go to college, the new freedoms of this world give Rebecca a taste of freedom and terrify Hephzi, exposed to the stares and taunts of the other student. However, both sisters hide the secret at the heart of their lives, and the truth of Rebecca's death is revealed step by step. Made me cry, and there's not many books do that.