[Flyboy]

My first thought that the woman was the Watcher, who has a propensity to turn up when the Doctor re-generates, or even the White Guardian, but observing the Doctor's re-action when she uncovered her face, he appeared to have a familial concern about her, or at least someone to whom he felt close to. I thought that she might be his mother and the make figure (yet to be revealed) was his father. I like the idea that she might be an older Donna, taking the role of an "honorary" Timelord, due to the meta-crisis, but that would not work with the concept of the time lock. The Doctor would have been aware of her presence at the time of the war.

I most of all like the idea that it might have been Romana, from I can remember, she secured a seat in the high council and subsequently was elected President (or was that a YouTube ep?). If I am wrong, she is still in "N" space and therefore not involved at all.