Zoria

You may be looking for Agent (Is anyone receiving these transmissions?).

During an adventure which they were forced to repeat at least one million times by a time loop after entering the Time Fracture, a human learned "Zoria's secrets". The Doctor was also aware of these. (PROSE: Hello And Congratulations!)

Behind the scenes

Zoria was a major character in the Time Fracture interactive story, where she was presented as a Time Lady from the Last Great Time War, scheming to resurrect Rassilon. Depending on the performance, she was played by Ivy Corbin, Jessica Hern or Chioma Uma.

In the webcast Is anyone receving these transmissions?, Robert Dudley makes reference to an agent who is gathering parts to build something. With the context of the Time Fracture play, the agent is clearly Zoria, who was revealed to be gathering components to construct a "Temporal Disruptor" to reset the universe so the Time Lords could preside over a new one.