The Mud Witch of Verdun (The Mud Witch Series Book 1)

In 1905, Addy’s grandmother took her away from home to the mysterious Order of the Sirenes. But it's 1915 now and she's leaving the Order to go to the Western Front to save as many lives as she can. But someone else has broken their vows, too. Will she be able to find the oathbreaker and overcome their superior power with her humble brand of magic?