There was a Terrance Dicks penned short story in, I think, the Radio Times 20th Anniversary edition which frames Susan as an important Gallifreyan political figure who the Doctor is hiding while pretending she's his grand-daughter. (Hopefully I've got that right and am not mixing it up with something else - I know there's also a story (possibly the same one) where Susan's Gallifreyan name is translated as Rose).