"Jemima" was the name taken by a Zygon who disguised itself as a seven year old human girl alongside its fellow Claudette. Together they served as the Zygon High Command based in Drakeman Junior School as part of Operation Double, the resettling of 20 million Zygons on Earth organised by the Unified Intelligence Taskforce and the Zygons.
When the ceasefire started to break down, "Jemima" and "Claudette" were approached by the Twelfth Doctor who had been alerted to the Nightmare Scenario. However, they were captured by members of a radical faction of Zygons called Truth or Consequences who believed that they had been betrayed, considering the two commanders to be traitors as they established a new High Command. In a video message sent to UNIT, "Jemima" and "Claudette" were ordered to normalise, returning to their true Zygon forms before being immediately executed, their bodies reduced to ashes with the rebel Zygons establishing themselves as the new Zygon High Command. (TV: The Zygon Invasion)