Sorry you are having problems. Ok when the girls got the bath was it for lice/mites with medication for it or just a clean up of dirty girls? What did you use?
The Bantam have you checked inside her vent to feel for egg that she may be having a problem passing? Massage gently toward vent, to help expel egg, give a tums or calcium to help. She may not like it again so soon but soak in warm water to help relax muscles in water at least up to bottom of wings vent covered with water. Massage toward vent. Dry her very well, can take 24hrs for a soggy chicken to dry out.
Her poo any sign of blood or anything else odd about it? Her breathing any signs of mucus nostrils, eyes, mouth? She eating drinking or faking it?
I would seperate her inside if possible to watch her. Check if eating, drinking, and so could see how her poo looks without having to sit and observe her with the flock. If possible take a pic of her and poo. Hope others step in with more advice soon.
Sorry about your chicken. You have had it tough with the fowl pox, and diarrhea in the one chicken. Did you ever treat them for coccidiosis when the hen had diarrhea? Puffing up can be a sign of cocci, but also of a sick cold chicken. Gasping can be a sign of infectious bronchitis, aspergillosis (from mold) and some of the other respiratory diseases. Here is a link about the respiratory diseases--look at bronchitis, MG, coryza, ILT, and aspergillosis: http://edis.ifas.ufl.edu/ps044