Kameron Hurley: God's War: Bel Dame Apocrypha Book 1 (Bel Dame Apocrypha, 1)

Nyx had already been to hell. One prayer more or less wouldn t make any difference... On a ravaged, contaminated world, a centuries-old holy war rages, fought by a bloody mix of mercenaries, magicians, and conscripted soldiers. Though the origins of the war are shady and complex, there's one thing everybody agrees on-- There's not a chance in hell of ending it. Nyx is a former government assassin who makes a living cutting off heads for cash. But when a dubious deal between her government and an alien gene pirate goes bad, Nyx's ugly past makes her the top pick for a covert recovery. The head they want her to bring home could end the war--but at what price? The world is about to find out.