Heaven's Fallen. Mantles of Power, #1

Fallen, but not defeated. Betrayed by those she trusted, Isalla was cast down from the heavens and into the heart of the hells. Bereft of her wings, the angel was rescued by Kanae, a demoness who challenges Isalla's belief of what demons should be. She has little choice but to accept Kanae's help, with as far from her homeland as she is, and slowly she begins to understand, then even admire Kanae. Unfortunately, the forces in the shadows have not forgotten Isalla, and they are willing to target anyone close to her, no matter how highly placed they may be.
As their long reach threatens to snuff out Isalla's life, Kanae proves a stalwart ally, and willing to face any danger beside her. It's an immense surprise to Isalla that in the depths of the hells she can find hope, allies, and possibly even love.