Lord of the Underworld by Skyler Andra

Hades messed up. It’s his fault the Lady of the Underworld left…again. The guy just can’t keep a good goddess down. But the Lord of the Dead can’t mope about the Underworld while it tears apart. Breaches in the fabric of the afterlife have allowed souls to escape and return to their lives. Something is wrong, and Hades needs Autumn’s help, for her to become the death goddess to figure it out.
After Hades hid who she really was, Autumn no longer wants anything to do with gods, death or the goddess awakening in her. That’s why she hightailed it to Fiji, to grow tropical flowers and eat pineapple and coconuts all day. But when Hades shows up with a bargain, a way to severe the connection between them, to free her of the grief of missing him and longing for what they had together, she agrees. Only Autumn will have to dive into the death goddess side of her, a side of her that has already killed, a side that terrifies her. When life and death collide, there can only be one winner.