Guinevere Winchester, also known as simply Guin, was a companion of the Doctor.

Guin accompanied the Doctor when he was sent by the Time Lords to the Schrödinger Institute, a research station in deep space where sabotage had caused a temporal echo to occur. The temporal echo meant that the Doctor and Guinevere could not be seen or even touch anything until someone else did so. The Doctor managed to rewire a control box after an echo of Tasdevin had worked on it. This broke the echo, allowing the Doctor and Guinevere to leave. (PROSE: Revenants)