Bioshock 2- Tenenbaum :Possible Spoiler:

So, has anyone else noticed that she completely vanishes from the game after your face-to-face encounter? I'm playing through my second game now "evil path" so can't say for sure if that is still the case; however, I'd figure that she would have had a larger part. There might be some tapes I skipped over, but I guess they're going to tie in her absence into Bioshock 3.:? Any thoughts?...

I Had the same problem and i guess i kinda solved it...

Well Tenenbaum left to do other things and help others as she states to you before you lose contact with her, and she leaves u with sinclair whom she promises will help you on your journey... My assumption is that she went around to save more littles sisters... or at least nab the ones you save... or get help from a friend to save these sisters.

Now that my theory, dont know if its the truth but its all i got.