The Forever King by Ben Galley
In Emaneska, to consort with magick is to court death. Banned by the Arka Empire, magick's purging has finally brought peace to a war-torn land.
Like any dutiful citizen, Mithrid Fenn wants nothing to do with magick. but when an illegal spellbook washes up on a beach after a battle between giant, unknown ships, Mithrid Fenn is thrust into a war she never knew existed. Her family slaughtered, Mithrid finds herself hunted by daemons and the emperor's assassins. She is dragged inexorably north to Scalussen, where mages, dragons, beastpeople, and witches doggedly wage a war for freedom against the tyrannical empire.
But Mithrid only cares for revenge and nothing nobler. If killing the emperor means helping the Outlaw King, then so be it. Even if it means drowning the world in fire.