Her name isn’t really Darcy, of course: her true name is something much older and a damn lot more powerful. Norse gods weren't the only supernatural beings in New Mexico when Thor was there.

They send Azrael to fetch him because he will not listen to anyone else. “Brother,” Azrael says. “It is time to come home. Your vessel is ready to be claimed.” The being that calls himself Eliot Spencer turns to the Angel of Death and replies, “I’m busy; already got some plans. Come back later.” That is the first attempt, but nowhere near the last. [AU during season 5 of Supernatural]