The Serpent and the Firefly - Davis Courtney

Sometimes you have to take control of the prophecy.

The prophecy says she'll destroy him, but if he doesn't reveal too much, will she help him rule Hell?

Jade is in witness protection and finds herself in possession of a store full of magical items. Her presence there alerts her existence to Baal, a serpent shifter and the first king of Hell. He arrives to kill her before she can become what has been prophesied and kill him, but he is enchanted by what he finds. She is everything he feared she would be, but she is also enticingly beautiful and pulls at something deep within him. She has no idea what she is, and he decides to try and use her for his own plans. 

Jade tentatively trusts Baal as she embraces her new powers and his reasons for seeking the keys to a gate in Hell. She agrees to help him, but along their journey she discovers that four planes of existence have crashed together; the fae realm, the angel realm, the demon realm and the earth realm. They are all fighting for control of earth and its inhabitants. 

She is the one prophesied to choose the winner. She is the one prophesied to kill the first king of Hell.