Berserker

Hanne carries the Nytte, an ancestral Viking blood-gift, and hers manifests as the Berserker curse: when she or someone she loves is threatened, she becomes an unstoppable, lethal fighter with no memory of what she's done.

After she kills three men attacking her father, Hanne and her three siblings flee Norway for the American frontier, searching for the uncle who might teach her to control the power before it controls her.

Guided by a cowboy named Owen, the family crosses the 1880s West pursued by a Norwegian baron who collects people like them, facing wild terrain, winter storms, and the long arm of the law along the way.