She was abducted by the War Lords and hypnotised into participating in their simulated version of the war. She and Lieutenant Jeremy Carstairs broke their conditioning thanks to the Second Doctor and they helped him fight the War Lords. She, like all the surviving victims of the War Lords, was returned home by the Time Lords. (TV: The War Games)
The Second Doctor met Lady Jennifer and Lieutenant Carstairs again in 1915, wanting to confirm that they had been returned to Earth safely, quickly ascertaining that they had no memory of having met him. The three of them helped Winston Churchill escape from the Players who had captured them, with the Doctor staying behind to keep the Players at gunpoint while the other three escaped in a plane that would have taken Churchill to Germany, the Doctor advising Carstairs and Jennifer to recognise that they were made for each other.
Over the next two decades, Jennifer and Carstairs were eventually married, with Jennifer dropping her title (although she jokingly commented that she was waiting to use it again when Jeremy got his knighthood). She later met the Sixth Doctor when he collaborated with Churchill and Carstairs to thwart a Nazi coup of Britain, although he posed as a different man to avoid awkward questions. (PROSE: Players)