Sondra Hagen is the mother of Basil Hagen and widow of Cassius Hagen. She's been mentioned a few times with implications that Basil and her aren't that close.

Sondra works for the Brigadoon Theater Company, a travelling theatre company and as such is only home once a month.

Sondra briefly appears at the end of the eleventh chapter of Stranger in a Strange School: "The Cold", where it is implied that she is connected to the prank conspiracy.