Fire Heart by Emma Hamm

They handed her a sword and bid her to take a throne…
Lorelei is half elf in a kingdom where that bloodline is synonymous with “slave”. The Umbra King holds everyone captive with his pet dragon who knows no mercy. She hides in the shadows and steals to stay alive, until a rebel group gives her an offer she can’t refuse.
The King seeks a bride. If she can get close enough, she could drive a dagger into that wicked man’s heart. But the bridal games are more difficult than most. Lorelei must prove herself not only beautiful, but talented, poised, and deadly as the king. However, the closer she gets to saving her kingdom, the more she realizes a singular problem stands in her way.
The dragon.
The King’s bodyguard is more than a slathering beast. He’s a man. And the longer she’s near him, the more she realizes that perhaps the king isn’t the most dangerous person in the kingdom. Perhaps she had to guard not only her body, but her heart. For a dragon mates for life, and they’re hard pressed to give up their treasures.