The Scent of Shadows: The First Sign of the Zodiac by Vicki Pettersson

When she was sixteen, Joanna Archer was brutally assaulted and left to die in the Nevada desert. By rights, she should be dead. Now a photographer by day, she prowls a different Las Vegas after sunset—a grim, secret Sin City where Light battles Shadow—seeking answers to whom or what she really is . . . and revenge for the horrors she was forced to endure. But the nightmare is just beginning—for the demons are hunting Joanna, and the powerful shadows want her for their own . . .