I really hope that she is not The Doctor's wife and I also hope that she is not The Doctor in a future regeneration. I don't know what she is, but I will pretty much be happy so long as she is not those!
Can't be a future regeneration. I know they did that mock up thing for BBC children in need where he meets Peter Davison in that god-awful outfit he wore, but in "fathers day" (series 1 or 27, depending on how you look at it, broadcast in 2005) he says that you can't cross your own time line.
Although when you think about it, he wouldn't really be crossing it. Just, meeting along the way?
Plus if she is a future incarnation of the doctor, why does she have that poxy book with all the crap they've done in it?
Heck - I figure she can't be a future Doctor because she's a woman. I figured that male Time Lords regenerate into men and women into women. But I have heard others speculate otherwise. But what do I know? I am new to all this