Mrs Fisher was the mother of David and Kirsty Fisher. She suffered from Munchausen by proxy, and loved the attention she got as the mother of a sick child. Kirsty believed her mother put things into her food to make her sick. When Mrs Fisher took Kirsty to Dr Rochford, he tried to convince her that Kirsty wasn't sick, but Mrs Fisher had done her research and kept asking for new medical tests to perform on Kirsty.
Mrs Fisher mostly ignored David. He believed that she was unaware that he had gotten involved in a gang.
After Kirsty had an adventure with the Seventh Doctor and Ace, she told her mum about it. Mrs Fisher seemed thrilled, excited that Kirsty would have to see experts and take more tests. (PROSE: Monsters)