“She’s initially presented purely as a foible for the protagonist—seductive and active where Angharad is submissive and passive. Like your two-headed goddess, Saints Acrasia and Amoret. As Myrddin mentioned in the letter. But eventually Arethusa becomes an ally. It’s a very clever subversion of the trope of the malevolent seductress.”
"Foible"? Author meant "foil".
