Perhaps they're hiding? And, if they're like the Doctor, they'd hide in the last places anyone would expect.
So we went looking: We figured that, regardless of where they were, they would have a general disregard for the laws of time and space, as well as at least one item that was bigger on the inside than the outside.....
She's dismissive of the laws of nature, and arrives and departs mysteriously. She has a bag which is clearly a lot bigger on the inside: Time lord technology, if not a TARDIS wearing an unusual disguise.
In the books she is known as 'The Great Exception' which follows the pattern of Time Lord names (The Doctor, The Master, The Meddling Monk ect ), and she is able to travel to alternate realities.
And, like The Doctor, the Poppins of the books hides her benevolent nature behind a stern, vain exterior.
We're betting that if you check her passport it'll say 'Gallifrey'
In case you don't recognise this guy, he's a character out of the Mickey Mouse Universe. He's got a Time Lords odd eating habits (mothballs are his favourite), he's happy to admit that he's a time traveller and possibly an alien. And (Ahem - we know where you'll go with this) his trouser appear to be much bigger on the inside.
The terribly un-Disney image that conjures up aside: It's probably unconventional for a Time lord to actually wear his TARDIS, but as far as we know there's no actual rule against it, and a TARDIS can disguise itself as anything......