IIRC, the Doctor said his family was dead. All Time Lords are citizens of Gallifrey, and not all citizens of Gallifrey are Time Lords. And a person doesn't need to be a Time Lord to open the TARDIS doors. My point is this - Susan might not have been a Time Lady. She may have her homeworld without attending the Academy, which seems to be the place where a person becomes a Time Lord or Lady. I think Susan died on Earth.
The Classic Who implied that the Doctor, the Master, and the Rani weren't the only Time Lords to leave Gallifrey. We had the Monk and a friend of the Doctor, mentioned in "Planet of the Spiders", and all those killed by House. It would have been nice to have expanded the list, and create a new villain.
I have heard it said that Moffat has no plans to bring back the Rani. I don't know why he is against bringing back this character.