Pictures of the pullet standing might be helpful. It could be a leg bone deformity such as vaurs or valgus deformity. Here are some links about that:
https://www.merckvetmanual.com/poultry/disorders-of-the-skeletal-system-in-poultry/noninfectious-skeletal-disorders-in-poultry...
Her feathers below her vent seem to have been pecked out. Did she have tail feathers? Or is she molting? That may be it. How old is she? They usually start to molt around 18 months old give or take, and molt yearly thereafter. Offering some extra protein if ahe is molting would be good. Feather...
Do her toes on the left foot curl under? Was she vaccinated for Mareks disease? Can she get to her food and water okay? I would probably keep her in a pen or crate near food and water.
I have made some one piece hen saddles out of thin polar fleece which don’t require sewing. I took a 7x8 piece that would cover the back, and cut 2 2 inch slits for the wings which hold the saddle on. They can be trimmed down to size. There are some pictures online.
How old is the chicken? When a chicken loses a lot of feathers it may take until the next big yearly molt for the feathers to grow back. Do you have any pictures of her? Would a hen saddle help to cover any bare spots?
I suppose it is too late to return the pullets to the seller? Have the new ones been with the existing birds? What antibiotic are you using? Do you have a picture of the worm you saw in the poop? Which wormer and dosage did you use? I would close your flock to new birds. It is not necessary to...
Eye injuries can be common with chicks. Irrigating an eye with saline and using either Terramycin eye ointment, Vetricyn, or plain triple antibiotic ointment into the eye twice a day might help. Hold a small scoop up to her beak, and dip her beak into it to drink and eat some. Let us know how...
Luckily, fowl pox is a limited virus, and is spread by mosquitoes primarily in hot weather. It lasts around 3 weeks in the dry form which causes scabs on the comb, face, and wattles. There is no treatment. More rarely one may have wet or diphtheritic fowl pox which causes yellow lesions inside...
I think the key to her problem is the she is 5 years old and “she laid 3 malformed eggs early on and has not laid an egg since.” She has probably been laying internally, and may have salpingitis and egg yolk peritonitis. Hard to know really until after she passes away and you can do a necropsy...
Adding new started birds from another flock is how many get a respiratory disease into their flocks. Symptoms can show up with a few days to weeks after exposure to carriers. They could have had the disease or just been exposed to it previously. Can you clean off any drainage, mucus or feed...
It can be difficult with your grandparents also taking care of the chickens. Hopefully they will get along well. I usually have raised my younger birds with older, but they have been separated with fencing or in a pen where both groups can see each other. Once the younger ones are the same size...
The one in post 5 does look like pictures I have seen of ocular Mareks. In the first picture, I had thought that one may have been an injury, but with the last pics, it may well be Mareks. The pupils should constrict (get smaller) when light is put into the eye, not dilate (get larger.) I would...
Chickens don’t get colds, but they get respiratory diseases such as infectious bronchitis, mycoplasma gallisepticum, coryza, ILT or others. They can get one disease such as IB, and it can be complicated with a second diseases such as MG or others. Can you return the rooster? That would be the...
Stress can be a common cause of abnormal eggs. This article shows common causes for some of the egg shell problems we may see:
https://www.backyardchickens.com/articles/common-egg-quality-problems.65923/
Her crop would normally be full in the middle of the day. Are you checking her crop first thing in the morning after she has gone all night without eating, to see if her crop is empty? She seems young for a crop disorder. When picking up a chicken you have to be careful not to accidentally...
Do her eyes look like the other chickens’ eyes when you look at them? At her age she could be having some reproductive problems that might affect her walking. Is she showing any signs of molting, which can bring on unusual behavior? How is her crop emptying by early morning? Is it empty and flat...