Sins of Eden. The Ascension Series, #7

The seventh and final book in SM Reine's USA TODAY bestselling Ascension SeriesThere have always been three gods. Always. Until Elise Kavanagh murdered them. A demon named Belphegor has entered the Origin and become a new god, triggering genesis: the death and rebirth of the entire universe. He wants Elise to join him in Eden for the end of all things, but only once she's watched everyone she cares about die painfully under his heel.
With nothing but a dwindling army of werewolves, Elise must enter Eden, slaughter Belphegor, and stop the genesis. But Belphegor's smarter than Adam ever was, and far crueler. He's spent lifetimes preparing for this. He will have his world of Hellfire. He will have victory. And he will have Elise's life.