Shades of Smoke and Shadows (Crooked Crowns Book 1) by Celia Ralk

When strange marks appear on Clara Afron's body, this is what she
fears most. The whispers and prophecies of nightmares and terror.
After successfully ignoring the marks for almost a year,
Clara is thrown back into a world of uncertainty.
The ruthless king takes her into his castle, under his soldiers' wings
and has his staff teach her and train her, clothe her and feed her.
Keep her safe.

But Clara doesn't know who to trust - not with her secrets or her abilities,
much less her life. As relationships grow
and power builds, secrets are shared, but there are more questions
than answers and the illusion of safety is shattered.

Clara fights to stay alive but her life quickly becomes a tailspin of
beautiful, powerful, welcome darkness.