Something So Lovely - The Neutrality Saga, #1

Kalliope has been content spending her days in Heaven's library with her best friend, not that she was given a choice. Unable to leave and with no idea where she came from, answers are not forthcoming until she finds herself in the path of Emmanuel, the first evil in creation, and his ambitions to replace their long absent God. Kalliope finds that she is all that stands between the Realms and Emmanuel's desire for destruction.
Thrown headfirst into a destiny kept hidden from her, she now must ascend the deserted throne of Purgatory and harness a rare power she never knew she held. Her saving grace comes in the form of a flirtatious prince of Hell, Asmodeus, whose immediate attraction to her serves as an attractive distraction from certain ruination. A figure from her missing past, she is immediately taken with him and finds solace in his arms.
He comes with his own set of problems, though, as his secrets might just be Kalliope's undoing. Kalliope's problems only start with Emmanuel, as he might not be the only one the Realms need saving from when her fear takes hold and the temptation of taking godhood for herself instead of fighting sounds too good to pass up.