She had spent decades looking after the library and had no children. She let the Kaballus Kids hang about in the library, telling them stories and giving them Grovian doughnuts. A psychic being called Sashana tricked Matildus into believing Sashana was her granddaughter. Sashana "psychically chipp[ed] away" at her for months, making Matildus doubt herself, and blocked Matildus' memories, making her memory appear to fail. This was part of a plot to have Matildus pass on custody of the archive to Sashana so she could sell off the library's collection. Because of Sashana's interference, Matildus began acting strangely, and had the Kaballus Kids barred.
Bill Potts revealed Sashana's deception, and told the Twelfth Doctor, Matildus and Sashana to stop whatever it was they were doing. Bill took a photograph on her phone which revealed Sashana's true form. She began to fry everyone's brains with her mind, but was stopped after Bill summoned the Ristallian crater-hound Archie, whose simple brain couldn't be kept back. Sashana was arrested. While Matildus believed that she had no family, the Doctor disagreed, pointing to the kids playing in the library. (COMIC: Matildus)
During the Doctor and Bill's attempts to work out the reasoning behind Fey Truscott-Sade and the Clockwise Men's attacks, they and Annabel Lake travelled back to the Archive. Again bursting in without Matildus' permission, Lake helped her recover a copy of Peter Pan, which the Doctor read and used to contact Fey in the Dreamspace. (COMIC: The Clockwise War)