"nor would she let Wednesday or Shadow look at her face."
Mask of Medusa
GNU Free Documentation LicenseMask of Medusa - Credit: Christoph Wagener

Gaiman hints that the woman in the darkened room is a Gorgon from Greek mythology.

She keeps dead mice and crickets in her fridge, presumably to feed to the snakes which form her hair. In legend, if you look on a Gorgon's face you are turned to stone.