Pillar of Ash by H. M. Long

Yske, a healer and daughter of the warrior priestess Hessa, holds the balance of power in a world-shattering war of the gods, in this thrilling, mythical and emotional epic fantasy saga.

The enthralling conclusion to the HALL OF SMOKE saga, perfect for fans of Ragnarök, Claire LeGrand, Margaret Owen, V. E. Schwab and Melissa Caruso
Yske, daughter of the legendary warrior priestess Hessa, has dedicated her life to medicine and pacifism in service to Aita, the Great Healer. When her twin brother Berin, hungry for glory, gathers a party to investigate rumours of strange sightings in the Unmade - shadows in the darkness at the end of the world - Yske joins the mission, to keep him safe.
Their journey east takes them through primal forests, walking paths last trod when gods were at war and ancient, powerful beasts were defeated and bound. And the closer they get to the Unmade, the more strange and terrible things haunt them from the shadows, corruptions in nature and monstrous creatures of moss and bone.
Earning the respect of Berin and his warriors, Yske must forge a place for mercy and healing in a world of violence and sacrifice. She must survive murderous ambushes and brutal sieges and take her place at the centre of the oldest war of all.
Thrust into a desperate conflict of survival, Yske and Berin will wage the final war with the gods - in the shadow of a vast and ancient tree, the fate of creation is about to be decided.