I had the same thing happen with my polish, who is doing fantastically now and being a bully.
Here is the thread:
https://www.backyardchickens.com/forum/viewtopic.php?id=149517 and regarding her lack of appetite,
https://www.backyardchickens.com/forum/viewtopic.php?id=153042
I used baby parrot formula (Called 'Exact' at
Petco and the other local pet store) that was about $5 for a bag, and got a plastic feeder syringe ($2) to feed the baby by hand. I left her in with her pals, where she lay in the corner and slept most of a whole week...I was not very optimistic.
She perked up and started eating when the others did, so I let her, and she's great now, but it wasn't as quick as all that. I fed her 4 or 5 times a day by hand, as she wouldn't fill her crop- just snacks.
I added vitamins to the feed the first few days, plus honey I nuked in case of contamination. I also tried to feed her scrambled eggs, but she didn't eat a lot of that, either.
I did put her on fake fur in her brooder so the other leg didn't get all sore, as it was initially. I had her separate for a few days in case of other causes.
Best of luck and keep us updated!