Gunwitch: A Tale of the King's Coven. Rose Bainbridge, Gunwitch, #1

In 1718, in an England that might have been, the law found Rosalind Bainbridge guilty of witchcraft. In lieu of execution, she became Private Bainbridge of the 101st Pistoleers... A Gunwitch of the King's Coven. Twenty-four years later, dishonorably discharged and working as a scout on the Amerigon frontier, Rose's past comes looking for her. A summons and a request from the officer who saved her from the hangman's noose.
A reunion with another veteran of the 101st, someone she never wanted to see again. And a meeting with the Misses Janett and Margaret Laxton, the daughters of the man who pressed her into service as a gunwitch. Reluctantly, Rose agrees to take Janett and Margaret to their father at Fort Russell. No one knows the swamps around New Venezia better than Rose and her bloodsister, the enigmatic Chal. The trip should take only a few days.
But there's more waiting in the swamps than mud and mosquitoes. War and betrayal threaten Rose and the girls, while an ancient, unspeakable evil pursues them all the way to the walls of Fort Russell.~ ~ ~ ~ ~The World of GUNWITCH: A TALE OF THE KING'S COVENThe world of Gunwitch: A Tale of the King's Coven resembles the middle period of colonization of the New World.* England, the Netherlands, and the other powers of Europe have crossed the mighty Atlantic Ocean in wooden sailing ships to stake their claims on North Amerigo, and to fight wars over those claims.* Once great Native Amerigon tribes, decimated by disease and the firepower of the Europeans, live like ghosts in the land they once ruled.* And African slaves have been imported to build and harvest and do the other work that translates into riches for their masters.
After that, though, you might start noticing the differences:* Steam-powered paddle boats navigate the interior waterways and lakes of the New World.* Steam-powered, semi-autonomous mechanical men called "grunzers" are used for heavy lifting of cargo on docks and of large-bore weapons on battlefields.* And, by an Act of Parliament in 1668, England stopped burning witches. Instead, both men and women who are convicted of witchcraft are conscripted into the newly formed 101st Pistoleers.
In the 101st Pistoleers, also known as the King's Coven or "the witches crew", the gunwitches--and gunlocks--are trained to use their magic for war. It's a whole New World.