Veiled in Darkness — Valerie Twombly

The story continues:
When Eli spots Ashley across a bloody battlefield, he can only steal a moment alone with her. Powerless is an emotion new to the hunter, but it's one he faces daily when he realizes killing the demon king in order to free his mate is out of the question.

Death was not a nickname Ashley wished to carry. Being the only one able to stop Lucifer's evil plan was an even worse fate. When she discovers her true ancestry, fear that she will succumb to her darker side forces her to dig deep for the strength she needs to fight.

The clock is ticking and soon Ashley will face the ultimate test.