Well that’s my interpretation, I’m not the writer but these things are well explained by Steve and Leah, since he once told she doesn’t use chthon’s power but his book (part of him) And clearly she used the destructive side of chaos(Darkhold) to end the black winter (she can manipulate its totality)

She didn’t even used her possibility form , that proves she doesn’t need that form to wields possibility, but she in the darkhold form uses more destructive potencial that is the chthon’s view of chaos as a concept

“EVEN THE ABYSS IS ENVIOUS OF THE THINGS I HAVE CONSUMED.” And the chthon’s projection, I think it was a reference for her living darkhold form , since the darkhold is made of chthon and she turned one with the book by consuming it .