Who does Athena disguise herself as in book 4?

In the context of the fourth book, I'm curious to know: Who does Athena, the goddess of wisdom and strategy, disguise herself as? Is it a mortal form that allows her to blend in seamlessly with the mortals, or perhaps a creature of myth and legend that serves her purpose? Her disguises often serve a strategic purpose, so I'm eager to learn what form she takes on in this particular instance and what role it plays in the narrative.