The ruthless lady's guide to wizardry - C. M. Waggoner

Hard-drinking petty thief Dellaria Wells is down on her luck in the city of Leiscourt -- again. Then she sees a want ad for a female bodyguard, and she fast-talks her way into the high-paying job. Along with a team of other women, she's meant to protect a rich young lady from mysterious assassins. At first Delly thinks the danger is exaggerated, but a series of attacks shows there's much to fear. Then she begins to fall for Winn, one of the other bodyguards, and the women team up against a mysterious, magical foe who seems to have allies everywhere.