Rose in Chains by Julie Soto

The war is over, the dark forces have won, and the hero who was supposed to save them is dead.

Captured as her castle is overrun by the enemy, Briony Rosewood knows that the world as she knows it is changed forever. The dark forces of Bomard have won and her people, the Eversuns, face imminent servitude, imprisonment or death. Her brother, fated to be heir twice over and unite the warring kingdoms, is dead.
Stripped of her Mind Magic and her freedom, Briony and the other survivors are quickly auctioned off to the highest bidders in an auction – and as the heir-apparent’s sister, she fetches the highest price.
After a fierce bidding war, she’s sold to none other than Toven a high ranking Bomardsun – and her long-time and ill-fated infatuation. Scion of a family known for their cruel control of Heart Magic, the Hearsts are ruthlessly ambitious, and Briony knows they will use her however they can to further their own interests.

Yet despite the horrors of her new world and the role she must learn to play within it, all is not lost. Help – and hope – may yet arise in the most unlikely of places…