This confirms my suspicion that Nina has not been in the Alternate Reality because of an unnamed specific reason.
HitFix: Have you gotten to play the Alternate Nina yet?
BB: Not yet. Not yet.
HitFix: Do you think there's a reason for that?
BB: This is a pretty heavily plot-driven show. So there's a reason. I don't know what it is, but there's a reason.
HitFix: If I asked you to guess, what would you speculate? It seems like her absence would be conspicuous at a certain point...
BB: Yeah. Yeah. So I would assume that means that there's going to be a very... Well, part of me's there. My arm is still on the other side. I keep wishing somebody would trip over it and go, "What the hell is this? Oh my God! This is Nina's! Let's take it back!" But no one has done that. They're a thoughtless bunch.
More of the interview can be found here.