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.
Sorry for your loss. Sometimes I will do a home necropsy to view the major abdominal organs just to see if I can guess what killed a hen. If you ever do one, take some pictures of the liver, intestines, spleen, gizzard, heart, etc, and note if there is any yellow fluid in the belly or a lot of...
Here is another site for the amoxytyl in stockif you prefer that:
https://birdpalproducts.com/products/tylomox-powder?srsltid=AfmBOoo9znjkZZAglu0f_gE69DjMUJkwBBipqWkYGBLgGjsxzVqeBJOE
Here is a link for amoxicillin capsules, and dosage is 250 mg orally given every 12 hours for 7-10 days.
https://www.dkhardware.com/fish-antibiotics-08644347-fish-mox-250mg-100-capsules-product-7955030.html?srsltid=AfmBOor6yR6XwGgE7BuxA0adVzSEizX_RRPadkdnyMT3qhREB5fzeRMheeY
If the chicken is sick, soaking could stress her so much that she could die. The only reason I would soak a chicken is if she had a vent prolapse or an extremely soiled vent, just a shallow soak, to clean her up. That would be done inside where it was warm, in warm water, and the chicken would...
Glad you could see the vet. They are always quite expensive but can be helpful. It sounds good that she is eating a little more. The antibiotic and anti-inflammatory pain med may be making her feel a bit better, and treat anything respiratory. Let us know how she is doing. You sound very...
The bile in the poop back in October could have been from liver problems (ie: fatty liver or liver problems from egg yolk peritonitis.) It is hard to know what is going on with your chicken. Sometimes we don’t get answers until a necropsy can be done if we lose them.
Does she have any yellow material inside her beak on that side or a bad odor? Sometimes canker can be inside the beak and protrude on the oitside. Also, I have seen a few of those turn out to be a tumor which a vet excised them. Is she eating and drinking okay?