It's been so long, but did they ever mention that baby again in the movies as they progressed? I seem to remember them putting it in some room or cocoon like a house plant because it was that "phase" but I don't remember anything about her after that. The birth of the baby was one of my favorite moments in the series but it seems like they just wrote her off after that as some sort of character mistake.
I seem to remember an interview with Ken Johnson from around '94 in which he said they were going to put Vessna in a cacoon and have her emerge as an older kid in alien makeup. Their reasoning was they couldn't keep making a new puppet every year, but they couldn't put a real baby in alien makeup. In the commentary for Dark Horizon, Johnson mentioned how bad he thought the puppet looked.
In Body and Soul, Vessna goes into the cacoon, but then they just never got around to bringing her back. You'd think George would remember giving birth to Vessna in "Real Men" and wonder what happened to his third kid. (Then again, George forgot males are the ones who give birth when in "Fifteen with Wanda" he lamented the fact that he wasn't there when Buck was born. Say what, George?!)