The Fire Wish (Jinni Wars)

A jinni. A princess. And the wish that changes everything. . . . Beautifully written and accessible fantasy for fans of Tamora Pierce, Rachel Hartman, and Laini Taylor.
 
In this romantic and evocative fantasy, Najwa is a jinni, training to be a spy in the war against the humans. Zayele is a human on her way to marry a prince of Baghdad—which she’ll do anything to avoid. So she captures Najwa and makes a wish. With a rush of smoke and fire, they fall apart and re-form—as each other. A jinni and a human, trading lives. Both girls must play their parts among enemies who would kill them if the deception were ever discovered—enemies including the young men Najwa and Zayele are just discovering they might love.