The Fall of Hades — Jeffrey Thomas

A young woman emerges from a catatonic state to find herself naked and devoid of memory, a centuries-long prisoner of an apocalyptic battle between formerly human avenging Angels, rebel bands of the Damned, and monstrous Demons of every description. With only a sentient, talking gun for a companion, she sets out to explore a radically transfigured Hell, her own surprising past, and the bulletproof fierceness of the human spirit