Sienna by Mel Teshco

He’s a bounty hunter sent to Earth to capture her. She’ll fight tooth and nail for her freedom.

Sienna Moore is a revered rare—a Strazan native with unique powers—who escaped to Earth with six other Strazanian rares from their vicious, Dronian enemy. Survival is now her only plan. After shifting into human form, she uses mind control to conceal her true identity. Except, nothing can stop the Dronians from closing in on her, or the bounty hunter from another planet who is now also on her trail.
Gray Bastine has only one goal: track down Sienna and capture her before the Dronians find and kill her. With his own planet in danger of becoming the Dronians next world to conquer and destroy, he’ll use force if necessary to get Sienna to tell him everything there is to know about their common enemy. A pity she isn’t so easy to acquire. The longer it takes to claim her, the more he realizes her safety is no less important than those of his own people.
Even worse, their attraction is making this a mission impossible.