Lethargic hen, napping and not eating

Red Sex link aged about 8 months, 4.5 lbs, laying since January, part of a flock of 5

She has been sick since Tuesday 4/12, today is Saturday. She was very lethargic on Tuesday morning and kept standing or sitting in one spot with eyes closed. Also had diarrhea. I took her to a vet and he said she does not have worms but gave her 10 day antibiotics in case of bacterial infection. I am giving her the medication and kept her inside house for two nights.

She seemed more animated and interested in food and preening on Wednesday and Thursday, less energetic on Friday. This morning she is again extremely lethargic and will not respond to talking or petting. She is hardly pooping now. I felt her crop and it feels kind of spongy. Can she be having fluid in there? She always did have a bulging crop that used to drag the ground, but recently she has lost weight.

A side note: we are having a rat problem since last weekend. It was seen inside the chicken run. I have boarded up entry points and have laid non-toxic traps around the yard for it, but I think it spooked the chcikens. the other chickens are now back to normal after some edgy behavior.

What should I do for her? Thanks for any suggestions. I feel that the sick chicken does not have very long.