Persephone would have died in Wermod Prison had Gwydion not insisted the Empyrean agents make the same offer to her. Although he never told her, she suspects and that is more than enough to buy her undying loyalty. That he is an excellent leader and recognises even well-hidden talent just sweetens the deal.
Nobody remembers her real name; they just know her as Persephone, she who welcomes the dead to the Underworld. Simply put; if Persephone has you in her sights, then you are already dead, you just haven't realised it yet.
Gwydion is rumoured to remember what the terrified blonde child he saved from rape and death with his improvised knife was named but he has told no-one.
Persephone herself either lost that part of her past to trauma or chose not to remember. Many suspect it is the latter because she was the first to cross The Line when Gwydion asked for volunteers.
Many say she has a special bullet she's saving for the moment she can get one particular man under her sights.