I expect she knew a later Doctor. Most likely, she saw a picture of the tenth Doctor. Her Doctor must have looked older, so we won't see her coming back anytime soon. Most likely, she will be seen in the comics, novels, or audio adventures or will be recast with someone younger when there is an older Doctor since he was obviously in her past. She probably didn't know the eleventh Doctor unless Matt Smith is the Doctor for many years. I suspect the 12th Doctor or another later Doctor will be older. I understand that had Smith not tried out early, the new Doctor was going to be older.
Marie, I'm so glad you started this discussion. I am (perhaps unhealthily) obsessed with River Song. I loved her character in Silence in the Library and thought the openness that she had with the doctor of the future was really refreshing in comparison to how most other companions feel toward the doctor. I loved that she was smart and energetic and I thought, "I can really see this person in a real relationship with a man who lives across time and space and being totally ok with all the craziness he gets up to." It looks like she'll be appearing in series 5, and while I'm really excited to get her back... I do wonder if maybe it's too soon. Perhaps I should just trust in Moffat's genius.
I think it's too soon for her. Also, something about her I didn't like. I think it was her openness with the Doctor that... weirded me out? I was unsettled by her familiarity with the Doctor, much like the Doctor was.
I'm hopeful that Moffat will be responsible with this relationship.
Wasn't she like his wife or some weird something or another....from the future? I didn't really like her character for some reason. Though, I'm intrigued by her and her having a sonic screwdriver which her version of the Doctor gave her, and the fact that she whispered his name, right? His real name?? Not real sure what to make of her, yet. There's only one event where he would ever tell his true name. Great discussion! Thanks for posting...can't wait to hear more theories.
She knows an awful lot about the Doctor though...........