The Wreckage of Paradise by Greg Stolze

Ten Seconds to Midnight

Sabriel, seductive fallen angel that she is, has been playing games with the souls of mortals and devils alike. The demons Hasmed and Usiel have both felt the sting of her tender mercies, but now they might be her only hope of staving off an apocalypse. The ancient creature called Avitu has decided that humanity, demons and all the universe want nothing more than oblivion, and it is getting ready to provide it. Can Sabriel prove it wrong?

Does she even want to?