In a perfect world, with her perfect friends, our woman was to live the dream life for all of eternity, already being immortal, and thus this transition to another form of immortality only reserved for the near dead was somewhat confusing, but then again, not really.
And so her sudden arrival to a large room filled with dimensional hardware and tools and parts and pieces left this woman very, very confused.
“Welcome TARDIS to the last true secret of the known universes.” a voice said in her head.
“Who is Tardis?” she asked more to herself than anyone else seeing as she saw no being in the vast room.
“You are, or will be soon enough.” replied the male voice before flooding her mind with information that would forever change her self-identity. It was instantly understood by this woman that should she accomplish this task, she would achieve immortality yet again, something that even her handler would not have. And so it was she set to work with the tools given to her, using nothing but her mind to maneuver pieces of the puzzle together, around a single beautiful design of glitter that fluttered frozen in time.
The timing of the building of any TARDIS is based on a single event, not any galactic need or desire. This event, so powerful and destructive that it is rarely seen is called Supernova, and when a Star goes Supernova, the energy output is both timeless and infinite. So harnessing this energy would truly make a being Supreme. Thus the secret of this knowledge is more protected than a universe with the Doctor in it.
And so it is that a TARDIS is born after only moments of work, for time is relative and very wibbly wobbly in this process. Now all that is needed, is for the Doctor to pick this TARDIS, which Clara would ensure in due course. The timeline is born, the stage is set and now it is the Doctor’s turn to perform for the universe.