The Elite
BOSS
The more interesting possibility is that Dr finds her on his travels, they do the whole Dr Who thing for a bit, then her season finale is when she ends up on that crashed ship on that Dalek wreck before the events of this episode.
Would be interesting to have a companion that we know is living on borrowed time, although that would kill a lot of the tension as we know she cant die until the moment that its her time.
I'd like that too.
The "remember" line just before Oswin looks at the camera was interesting though. Also, if she traveled with The Doctor why doesn't she seem to remember him? Post-conversion memory loss maybe?