Lilith's Arithmetic: The Revelations of Artemisia Wright. Eve of Light: Blood Noon, #2

Holy assassin or lab experiment - either way, the target dies. They strap her upright at a formal dinner party, in a gown she doesn't remember owning, and the man in the white tuxedo introduces himself the way he apparently must every time: I am God's metaphysician. Artemisia Wright is the private clinic's prize subject. Inside a chamber shaped like a half-buried silver skull, she hunts and kills the same teenager - session after session, death after death - and afterward the doctors patch it out of her memory and call the work a Cure.
But Artemisia keeps a secret no drug has reached. She believes she is the heir of Lilith, chosen to destroy a "son of Adam" before an insane God drags all Creation down into ruin. Her captors call that delusion. She calls it her mission. Somebody is lying - and it may be her own memory. Whatever the truth is, the abilities are real - and the clinic did not give her all of them. When the prize subject finally escapes, her freedom ends nothing - except the rehearsals.
Somewhere out there, her rehearsed victim - killed more times than he knows - is walking around alive. And Artemisia, haunted, hunted, and armed with talents no laboratory can explain, intends to finish the arithmetic. Told entirely from the killer's point of view, Lilith's Arithmetic is a literary descent into psychological horror - rewritten memory, weaponized faith, torture repaid, and a holy war that may have been built in a lab.
The truest horror is how easy she is to root for.