Thank you, I'm glad you've enjoyed it!
I'm planning on adding some mutual gainer personalities in the 'More Personalities' update that'll work as you describe. They'll reverse the 'I'll eat if you do' feeder fattening from the Polishing Update, similar to how the feeders were designed to be a reverse of the original game.
It does make sense that some girls would try to lose weight when left alone. I can look at that.
With the girls showing up at the facility, that might be because they're addicted to Dizzy's and have passively eaten their way to hyper obesity. I might put a cap on the passive gaining, as some of the dialogue assumes that you've fattened them out of Gentle Meadows.