Vow of the Undead by Elsa Frey

She has until first light to answer the Gods’ demands, or marry a monster.

Exposed as a witch and bound for execution, Silver refuses to show fear. When her defiance intrigues the king, he spares her life on one condition: *she becomes his wife. *
But belonging to the king is just as deadly. Because the royal court of Vylheim—a vast and brutal Viking world—is teeming with vampires.

With the Gods' help, she flees the arranged marriage only to find she can't escape the Gods from twisting her mind as she becomes their chosen huntress.

All it takes is one kill, and she’ll be bound to this duty.

With the king coming to drag her to the altar, Silver is ready to step into the Call of the Gods and become the huntress who can stop him, until she meets Kayn, and everything she knows about their kind unravels…including the king’s motives.

Now she’s falling for the enemies, when the only way to save herself is to kill them.