The Hanging Heart (Realm of Beating Hearts) by Eva Simmons

Elorie has never known anything beyond the magic-void prison island of Alyssium. She tends to the dead who are sent to the shore for burning, while living among the humans who help guard the Fae prison. Until one day, she rests her hands on a dead Fae prisoner's chest and accidentally wakes the most lethal warrior in the constellation of realms. Fascinated by Elorie's unique ability to resurrect such power, the King summons her to the Ley Court. He declares her to be his chosen, promising a union that will restore magic to a dying land. But the Fae she woke has other plans. As the rightful heir to a rival crown, Wilder doesn't want to heal the kingdom that locked him in a cell for a century, he wants to destroy it. And to do so, he'll claim Elorie for himself. Except magic can't be stolen, only offered. And in a war between crowns, Elorie is the only one who can choose how to bind her untamed power. Read more