Ash Princess (Ash Princess Trilogy #1) by Laura Sebastian
When the Kaiser forces her to execute her last hope of rescue, Theo can’t keep her feelings and memories pushed down any longer. She vows revenge, throwing herself into a plot to seduce and murder the Kaiser’s warrior son with the help of a group of magically gifted and volatile rebels. But Theo doesn’t expect to develop feelings for the Prinz. Or for her rebel allies to challenge her friendship with the one person who’s been kind to her throughout the last hopeless decade: her heart’s sister, Cress.
Cornered into impossible choices and unable to trust even those who are on her side, Theo will have to decide how far she’s willing to go to save her people and how much of herself she’s willing to sacrifice to become queen.