Promised in Fire by Jasmine Walt

A fae with impossible magic
Adara has been an outsider for as long as she can remember. Born and raised in the earth fae realm, she’s a water fae who can’t control her magic, making her not just useless, but downright dangerous at times.
When a training mishap accidentally unleashes a hidden magic inside her, Adara suddenly finds herself on the run. The king wants to use her powers for nefarious reasons, and he’ll stop at nothing to obtain her—including kidnapping and torturing Adara’s own mother.

A dragon awoken from slumber
As the last of his kind, Einar wants nothing to do with the kingdom of Ediria or its problems. The fae hunted his kind to extinction, and he harbors only hatred for them in his heart.
But when a beautiful fae female awakens him from an enchanted slumber, Einar is reluctantly ensnared. And while he would rather die than submit to any fae, every fiber of his body screams to claim her as his own.

A kingdom corrupted by darkness
The last thing Adara and Einar want to do is join forces, no matter how scorching the passion between them is. But a dark magic is sweeping through the land, rotting the kingdom from the inside out. And if the two cannot put aside the centuries-old feud between their races, they will lose everything they hold dear…