Demon Magic by Linsey Hall

Waking up in hell was not Del Devereaux’s idea of a good time. She’d rather be back on earth, killing demons and hunting down magical treasure for her shop, Ancient Magic. Fortunately, Del possesses a mysterious power over death. She’s got no idea what the power does and it scares the hell out of her, but it’s got to be good for something. Like getting out of hell.
Escaping hell is easy—it’s staying out that’s hard. Del’s magic defies the laws of the supernatural world. If others learn what she is, it’s a guaranteed prison sentence. And Del already has a deadly and forbidden secret—she shares a soul with a dragon.
When the Warden of the Underworld shows up on her doorstep, wanting to drag her back to hell, things get sticky. An escaped demon gives her an opportunity to win her freedom, but only if she teams up with the Warden, the strongest, and strangest, shifter that she’s ever met.

Del Bellator’s simple life of treasure hunting and demon slaying ended the moment she learned she was a Guardian between the Underworld and Earth. The only problem? She has no idea what that means and no control over the magic that could help her. Sure, she can turn into a Phantom and walk through walls, but in a world where demons can throw fireballs or strike her down with lightning, she needs control of some bigger magical weapons.

To make matters worse, demons are now drawn to her like flies to honey. She’s a walking, talking demon magnet. To save her own life, she must master her powers. That means embarking on a treasure hunt unlike any she’s ever conducted. Fortunately, she has the help of Were-demon and Warden of the Underworld, Roarke Fallon, along with her FireSoul sisters, Cass and Nix. As the clock ticks down, she can only hope it will be enough.