That yellow poop is fairly common with a reproductive infection of E.coli. It sounds like she is possibly too far sick to help. Were you able to order antibiotics? They may come in handy later even if you lose her. I have had quite a few hens die from reproductive disorders or infection, and...
Most antibiotics are very hard to get without a vet. Amoxicillin or enrofloxacin are ones you can use, and you might get one of those from a vet or online for pigeons. There is a national shortage of amoxicillin. Your hen sounds like she is having symptoms of a reproductive disorder or...