ASH: A Secret History by Mary Gentle
In a world not unlike fiteenth century mediaeval Europe ...For the beautiful young woman Ash, life has always been arquebuses and artillery, swords and armour and the true horrors of hand-to-hand combat. War is her job. She has fought her way to the command of a mercenary company, and on her unlikely shoulders lies the destiny of a Europe threatened by the depredations of an Infidel army more terrible than any nightmare. Ash is guided by voices. They may come from her God, or from a source infinitely stranger ...ASH: A SECRET HISTORY marks the full-flowering of the talent of one of the world's most acclaimed writers of fantasy.