I assume she went back to wherever she was during every single other visit the Doctor made back to Gallifrey. If the Doc wasn't close enough to drop in during ANY of his other visits, he's not really about to start now.
I know it was RTD who said that in his writer's mind, that woman was the Doctor's mother, but there's absolutely no dialogue or evidence to support (or refute) it. All we know is that she was a member of the ruling party of Gallifrey (though not necessarily the HIGH council, otherwise wouldn't she have been exiled with them on the next shuttle after Rassilon?), and that she was someone whom the Doctor knew and respected to some degree. Fans have thrown about the notion that she was Romana, Flavia, or even Susan, but until some writer definitely marks this person as such, she's no one we know for sure.
Mark