So happy to hear the antibiotic worked!
Yes, combs go pale and limp during molt due to the decrease in hormones. After laying begins again, the comb reddens and become larger and firmer.
If a chicken is very sick, showing severe symptoms, I treat for a full ten days when giving amoxicillin. Five to seven days with moderate symptoms.
I haven't seen any yeast infections crop up (pun!) with amoxicillin, but I'm all for the yogurt as a precaution.
The easiest and most accurate method of getting any form of meds down a chicken is to syringe it directly into the crop via the esophagus. There are two holes in the throat of a chicken. The one in the center behind the tongue goes to the airway. The other one, on the chicken's right side of the...
At the risk of sounding arrogant, I can probably give you as good a guesses as you got from this vet, not saying they weren't some help to you in narrowing down the hen's cause of illness.
Given her age and that she recently proved she's still laying, and mostly ruling out parasites, that...
Is she passing any cecal poop? Is her vent looking like it may be prolapsing (inside hanging out)?
What has she had to eat just prior to this trouble? Does she spend time digging in a compost bin? How about grass that has tough stems? Have you seen any bits in her poop?