Bride of the Witch King by Viola Grace

Training to be a queen, she just needs to find and enchant her king. Revenge can wait until she is settled.

Viika barely survived her first night at the bride school. Waking up to being nursed by a demon was hard enough, but having Emrie sooth and heal her took her by surprise. The world around her was not what she had been told. Demons were wise and powerful, wizards did not always know what they were doing. Witches were common for the powered folks, and Viika was an exception in the crowd.
Controlling her hatred for the vampires who had tortured her meant learning to see them—and judge them—as individuals. It was a life lesson that helped her through the following years.

Once she was grown, it was time to seek out her king or, rather, find a witch lord to raise to the position of king. He could only rise to power with a queen of his own, and she was willing to go shopping for her king.
After a false start she finds her match and sets about combining her power with his. It isn’t for the faint of heart, but he meets her advances head on, and together, they set about restoring the balance in the place she once called home.