Dread Nation by Justina Ireland

Jane McKeene was born two days before the dead began to walk the battlefields of Gettysburg & Chancellorsville—derailing the War and changing America forever. In this new nation, safety for all depends on the work of a few, and laws require certain children attend combat schools to learn to put down the dead. But there are also opportunities—and Jane is studying to become an Attendant, trained in both weaponry and etiquette to protect the well-to-do. It’s a chance for a better life.