Assuming stable time lines and no big reboots, she's from the Doctors future so post Time War, so there should be no other Time lords about to teach her. Either it was not a Time lord, it was a later regeneration of the Doctor (though she seems to know the different regenerations as the same person) or someone survived. what about the Rani? Romana? Drax?
Though the crack in the world, apart from spawning lots of 'amy's crack' jokes, may be foreshadowing a big dimensional collapse and plot reset.