Here is a good article on crop disorders:
https://www.backyardchickens.com/articles/how-to-treat-sour-crop-and-impacted-crop-and-how-to-know-which-one-youre-dealing-with.73607/
It sounds like it could be MG, but without testing, it would be hard to know. I would get Tylosin powder online and use 1 tsp per gallon of water for 5 days as her only water. Since Terramycin now may require a prescription, you can use a small dab of plain Neosporin or triple antibiotic...
If you get the ivermectin 5 mg per ml pour on, to the back of the neck over the spine, you can apply 0.1 ml per every 2 pounds of weight once and again in 14 days to treat mites. Permethrin garden dust can also be used once and repeated in 7 days to get the mites, and later the newly hatched...
Botulism is a sudden illness brought on by after eating a toxin produced by animal or plant products decaying in an area of no oxygen or anaerobic conditions. It causes sudden flaccid paralysis of the feet and legs, then wings, breathing muscles and upper body, resulting in death. This doesn’t...
They are so low in pecking order, the others are not letting them eat. I would take them aside in the am and just before roost time, and feed them separately daily, but then let them out with their flock to remain members. Separating them will probably cause it to become worse. If they can have...
I would agree that the first picture, it looks like peck injuries, and now the second one looks like fowl pox. I wonder if she developed the pox after she was separated? Where are you located, and do you have mosquitoes out now? Fowl pox usually lasts about 3 weeks, and most chickens recover. I...
I agree that she has some stridor. I would see that she is drinking some water. Stridor happens when something is partially blocking the airway, such as a small piece of feed, mucus plug, or swollen membranes. If you notice her developing more respiratory symptoms, such as sneezing, watery eyes...
Do you plan to drain it again? I might use a disposable scalpel blade ( from the feed store) this time to make a slit, done very carefully with someone holding her wrapped in a towel. Disinfect the area. Use some antibiotic ointment afterward.
Liver problems can sometimes cause jaundice and turn the skin yellow, but I don’t know if that is her problem. Liver disorders can go along with certain reproductive disorders or fatty liver disease.
Separate her from other chickens immediately. Her lower belly below her vent has been pecked open and cannibalized. Have you seen any vent pecking or bullying? Is there any way she could have been hurt by a predator? I would apply saline, weak Betadine or chlorhexidene to the wound. Then apply...
You could start the amoxicillin now, and use 150 mg since she only weighs 3 pounds. I would probably try to use roughly 1/3 of your 500 mg capsules. Divide it and mix with some cream cheese, peanut butter, or egg. The amox by itself may do the trick. Let us know.