An easy death / Charlaine Harris.

Set in a fractured United States, in the southwestern country now known as Texoma, in a world where magic is acknowledged but mistrusted, especially by a young gunslinger named Lizbeth Rose. Battered by a run across the border to Mexico, Lizbeth Rose takes a job offer from a pair of Russian wizards to be their local guide and gunnie. For the wizards, Gunnie Rose has already acquired a fearsome reputation and they’re at a desperate crossroad, even if they won’t admit it. They’re searching through the small border towns near Mexico, trying to locate a low-level magic practitioner, Oleg Karkarov. The wizards believe Oleg is a direct descendant of Grigori Rasputin, and that Oleg’s blood can save the young tsar’s life. As the trio journey through an altered America, shattered into several countries by the assassination of Franklin Roosevelt and the Great Depression, they’re set on by enemies. It’s clear that a powerful force does not want them to succeed in their mission. Lizbeth Rose is a gunnie who has never failed a client, but her oath will test all of her skills and resolve to get them all out alive.