Walker Between the Worlds: Book 1 of the Sibyl Chronicles

Her name is Ema. She walks between the worlds, from the darkness of an almost-forgotten past, a renegade prophetess that hunts with a living human, a 'pocket', those who are evil and have upset the balance of Divine Order as they navigate the waters of forbidden magic.In a nightmare world peopled by horrific beings, she stalks the most insidious, who thrive on agony and desecration. Many have themselves taken over human avatars, practicing necromancy and instructing them in destruction. However not all are vanquished, and await a chance to conquer the Walker Between the Worlds, even if takes hundreds of years to spring the trap.