An agent of Yatwer, just doesn't fit with what we know about her, though. Sorweel makes a natural enemy to Kellhus. Kel, the son of Yatwer's enemy? Yea, it sounds good and what better way to strike at Kellhus than using his progeny. But, then you're excluding the scene with Ajokli, the Trickster. And, just setting here thinking, it seems that this voice doesn't have any straight forward goals. It just seems to want to sow chaos. And that, IMHO, would align with Ajokli more than Yatwer. Those times it seems to help Yatwer's goals, I believe to be purely coincidental. And doesn't Kel's personality seem to be a perfect representation of a Trickster?