The fish flakes that you mention may work.
Some folks like @dawg53 use Tricide-Neo for difficult to treat Bumblefoot.
https://www.backyardchickens.com/threads/treating-bumblefoot-with-tricide-neo.513183/post-6526194
You can continue to feed chick starter or an all flock feed until they all come into lay, it won't hurt them.
Many people feed all flock period.
Just provide oyster shell free choice.
The legs are turning at the joints? Are the joints in place, can you compare them to other chicks her age?
If the joints are not out of place/slipped tendon, and they are turned, she may have a leg bone deformity. Valgus Varus.
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Can you post photos of your chicken and the poop?
Is this a hen or rooster? How old?
The chicken's left or your left?
If this is a hen, when was her last egg?
Can she eat/drink ?
For Scaly Leg Mites, apply an oil, NuStock Cream or Vaseline to the legs at least weekly to help smother the mites which live under the scales of the feet/legs.
Do you have photos of her feet/legs?
When was her last egg?
Do you have photos of her, the splotchy legs and her poop?
You treated for Mites, does she have mites?
Feel her abdomen below the vent between her legs, is there any bloat or feeling of fluid?
I'd work on hydration, get some sugar water into her. See if you can entice...
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Do you have photos of the sick hen and your setup? A video of her actions may help too. Upload video to youtube and provide a link.
How long have the new birds been next to yours? A month or two?
Have his birds recovered, became asymptomatic without treatment or are they all...
I'd put the 1/4tablet B-Complex right into the beak and let her swallow, same as the Extra Calcium.
Electrolytes are fine to give, but provide fresh water too.
Is he your only rooster?
To me he looks like he's been in a fight with another rooster.
I'd get some saline or make some, rinse his face really well with the saline and get all the debris and blood off. Work on getting his eyes open. You can rinse those with saline too.
Put a bit of...
No, don't withhold food or water, she needs to stay hydrated.
Can you look inside her beak for any Canker or lesions?
You mention a rotten smell to the beak, is there any facial swelling, mucous, watery or puffy eyes?
Photos of her bum and the vent gleet? Poop?
No eggs, except for Fairy...
Looks like the spots are just from losing the scabs and she's healing.
You can put a little triple antibiotic ointment on the scabs to help heal them up.
If she's in molt, she may have stopped laying until she's finished.
See that she's eating her normal feed and drinking well. If she's a...
If what was expelled is like the one that @pamiejune has pictured, it's an Intact Follicle.
See that the hens are eating a nutritionally balanced poultry feed and have oyster shell free choice.
There's not really anything you can do about an expelled intact Follicle, it's just an ovum that's...
I would start her on 300mg Calcium Citrate+D3 once daily asap. Give for at least 7 days. Calcium is important for retention, healing and contractions.
Soaking in an epsom salts bath may help if she will tolerate it. Keep the exposed tissue coated with the Prep H, Raw Honey, Hydrocortisone...
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I'm sorry to hear she didn't make it.
It would be hard to know what was causing her symptoms without sending the body for further testing through your state lab.
https://www.metzerfarms.com/poultry-labs.html?srsltid=AfmBOoo_ViMBMPTn-WWLiNxdDxo9vLOusHK3kaVahQq4-81NW6vJ9UrZ
Do...