Not long ago we all experienced a phenomenon of absolute unreal occurrence, the death of death itself. The Miracle. Clearly this phenomenon occurred through technology few have access too, perhaps only even Time Lord; and the only time-lord to conduct a pointless experiment like this would clearly be The Rani. The Rani has been shown to take a strong interest in direct observation of her experiments, an interest she could fulfill by using the alias of Jilly Kitzinger. The proof that The Rani is Jilly Kitzinger can be further inferred from the fact that they both enjoy the colour red, and that they both display startling amorality, and unparalleled genius.
Jilly, and in fact all the benefactors of The Miracle in Phi-Corp (The Three Families) displayed unparalleled villainous genius in their profiting off of it. Jilly and Phi-Corp eyed short term profit margins in spite of the fact that inevitable social collapse will make such profits useless. Further, Jilly does not express worry or resentment over the fact that inevitably a fate worse than death awaits her as well. Either this is because she is not the genius she appears to be, or, more obviously, because as a Time Lord Jilly does not have to worry about the perils of old age and disease and the Miracle doesn't affect Time Lords.
The Rani has previously used disguises to observe the successes or failures of her experiments directly. This occurred most notoriously during the Luddite rebellions, when The Rani masked her unparalleled beauty and genius with the outfit of a doddering old hag. While her current mask as Jilly may be more intelligent and beautiful it still serves the same purpose: to allow her to observe the effects of the miracle directly, and to possibly recruit potential test-subjects or servants, Oswald Danes.