Hecate

Hecate is a greek goddess of crossroads (particularly triple), witchcraft, and herbalism.

Description
A preolympian goddess of the underworld, Hecate is by extension associated with death and the night. She is often depicted as threefold, and as such it extends her protection to womanhood. She has often been conflated with the moon goddess Diana.

Skin Game
In Skin Game, Harry Dresden recognizes two groups of three golden statues in Hades' Vault as representation of her. Further, Hades mentions she has led Demeter around, as a wedding gift to him and Persephone, so they could enjoy a honeymoon without Demeter's cumbersome presence.