Maria di Angelo

Ms. di Angelo is the mother of Bianca and Nico di Angelo

Description
In the Sword of Hades, Nico's mother visits him the form of the goddess of ghosts, Melinoe. She is described by Percy as wearing a black dress with white glooves and pearls, with her dark hair pulled back. He couldn't make out her face.

The Last Olympian
More we be revealed about her in the last book, where her identity will even surprise Nico.