Mrs. Siebert is the wife of President Siebert, the president of the California Institute of Technology.
She and her husband have a teenage daughter. The family owns several dogs.
She was mentioned in "The Monopolar Expedition" (S2E23) when her husband sent Sheldon on a three-month National Science Foundation expedition to the Arctic Circle, and was annoyed when Sheldon visited his family at their home in the middle of the night. Mrs. Siebert eventually set their dogs on the unwelcome visitor.