Theory: Rosies true identity iiiiiiiis

Eve, or a fallen angel.

Both Adam Rosie have golden power. Angelic power is baseline Golden. A large number of angels followed Lucifer into hell in classic mythology. Rosie seems to never really close shop with what she is doing. As a proper full power demon/fallen angel she has the authority to reach out to the human realm to make contact with mortal souls (like Al)

Rosie isn't listed as a sinner, Because she's a full proper Demon, which would mean she's likely not Eve (unless we consider Adam who was mortal a full Angel).

To her Empowering Alastor is a trivial matter, As Even Rosie knows about the core power difference between an Arch-angel and An Overlord. But the thing is, overlords as big as they can get. If Adam and Abel are comparable in power and are Considered Arch Angels, that means Human souls in heaven are significantly more powerful than their hellborn counterparts. Which considering the fact that Lucifer is hells top dog, and he's not even at the top of the angelic hierarchy says a lot. Though the difference in power between the Goetia and Lucifer haven't been fully established.

Though, we have not seen Eve, who'd be a powerful sinner to begin with. Eve *should* be around, and would be on par with Adam in terms of power. Nor have we seen Cain (unless he's cursed to walk the earth as a vampire).