Althyn and the Othian Dagger

After her father pushes her too far, Althyn Laethwyn, who was raised in isolation by her mother on an unnamed island, grows into a dangerous tyrant to be reckoned with. As she travels from island to port to temple and even the watery underworld, her father's slave ever faithful and doting at her side, she discovers her true nature, and what a horrible revelation it is.