Demonblood Trilogy by Penelope King (epub) [BluA]

Book 1: A Demon Made Me Do It
Book 2: Fire With Fire
Book 3: Curse of Shadows and Light

Summary:
Five years ago, demons murdered her dearest friends and shattered her soul. Now she’s a human girl by day who transforms into a demon at night, driven by revenge. Cursed to live in a world where she doesn’t belong, she longs for the day she can return to her rightful life.

She didn’t expect to meet him. She didn’t expect to have to choose. And she didn’t expect that choice to cost her everything.

It’s good to be bad.