A Sublime Casualty by Addison Moore

In an attempt to escape her past, Phoebe Benedict steals the identity of a girl who has gone missing. She never meant to keep a secret so dark that it held the key to another hell entirely.
She never meant to say I’m sorry.

Lizzy Hartley disappeared over a year ago and is suddenly sending cryptic messages from beyond the grave. It’s hot in hell, and Lizzy wants Phoebe to know it.

Destinies collide as Phoebe hunts for the truth about Lizzy’s disappearance. Assuming someone else’s identity is proving far more dangerous than Phoebe could have ever imagined. And if she’s not careful, she might just join Lizzy in hell.

Excerpt
They say to commit murder is a crime against your soul as much as it is another person’s body—an everlasting burden. I say it was a relief—like lancing open my own throat just to breathe for the very first time. But one corpse led to another, and soon I left my own life to step into someone else’s. I never meant for things to go so far. I never meant to leave a trail of bodies in my wake. I never meant to keep a secret so dark that it held the key to another hell entirely.
I never meant to say I’m sorry.