Scarla by BC Furtney

Scarla Fragran shook the world. The youngest female kickboxing champion in history, she came from nowhere to become the brightest young star with the most promising future. Until it all died, along with the man she loved and the only life she'd ever known. Now, she hunts and kills, preying on the predators that cost her more than she ever thought she could lose. Working as an undercover prostitute for the police, she walks the night as bait. Her only lifeline is a man she hardly knows, but Facil LeTour is the only thing standing between Scarla and the jaws of death. Every night is a roll of the dice. She has nothing left to live for, but a million ways to die.