Fortress of Blood and Power by Rachel L. Schade

Sacrificed to the fae, her only hope is to run. But the cruel royals who seek her have never lost their prey.

Florentia (Ren) Cantwell has always been an outsider. The townspeople fear her and her unusual silver hair, spreading rumors that she’s not entirely human. She’s never believed those crafted lies—until a stranger causes her to manifest dangerous winter magic.
Determined to be rid of her, Ren’s brother casts her beyond their town’s borders, into the fae land of Silverfrost, leaving her as an offering to the cruel royal family. Ren knows that if the royals come to fetch her, she will face unspeakable horrors.
Accepting the help of Garrick Darkgrove, a handsome wolf shifter and fellow loner, she flees the royal hunters in a desperate attempt to reach safety.
But all goes wrong one heartbreaking night.
The sibling king and queen take Ren to their austere fortress, where she is entangled in a series of deadly trials meant to test her magic and her bloodline. She is a spectacle. A tool. A captive.
Forced to navigate a world of torture, manipulation, and demons, Ren knows she can trust no one. Not even Garrick, the man she now understands is forbidden to her. The one that, against her better judgment, she’s falling for.

She’s prepared to pay for her freedom—but when the cost is her heart, the price may be more than she can bear.