When the usual milestone inspection is replaced with a special scene with the manager, that marks the end of dialogue and description development for that girl. You can also verify if you're done by checking the noticeboard. You can continue to fatten her for more of the endgame currency, but you won't see any further changes.
Viewing post in Update 3 Post Release Bug Fixes comments
Thanks for the answer. I was hoping to see some signs of the chamber getting overloaded, the observation window cracking or something, but perhaps that can be done sometime later if you choose.
For now, I'll enjoy seeing how the different personalities react to the blob stages. The devoted and eager feedees are some of the best due to them enjoying the process so much, while the athletic feels a little depressing due to describing how much of a workout existing is, plus that gasped "Help..." at the penultimate stage.