Rocinante was the Time Lord ambassador to the Qwerm. The Qwerm trapped her inside her TARDIS and plotted to one day invade the universe and defeat the Time Lords. Rocinante placed the interior of the TARDIS in a time loop and trapped the Qwerm inside. She was midway through a regeneration when the time loop initiated, leaving one half of her an old woman, and the other half a small child.
Rocinante then signalled for another TARDIS to help her. River Song was the first to find her, and together they managed to trap the Qwerm inside the TARDIS forever by connecting the TARDIS' front and back doors together. (PROSE: River of Time)