I have a pullet(welsummer) that has the same problem that yours has. She was born May4th. She was fine when born then at about 2 weeks old she was limping then could not walk or stand.She could not put wait on her legs and her feet were gnarled We separated her from the others, fed her and gave water by hand. Made a chick chair that she was in for a few weeks. I read online and tried the infant vitamins and they worked after a couple of weeks she was running around. At this point she still looked like a little chick. She was able to feed herself and get water finally.Then she began to grow, got her adult colors and feathers..At this point she is still separated in a separate little pen next to the flock.It was looking like she was going to catch up to her siblings soon in growth.All was fine until a few days ago. She became wobbly and could not cheep like she used to(we call her Cheepers) because she was always so vocal.She makes this little sound like she is trying to cheep and shakes her head.Now she cant stand again. We are back to feeding her by hand.We started her on poly vysol again.We put Diatemauses Earth in her water. She has a great appetite thank goodness.Her feet are looking like they did before. She is on Nutrena feed and her coop is always very clean.The only thing I can think of is she needs more vitamins then the other hens at all times. I thought once her growth took off and she looked her age she would not need the extras, I guess I was wrong. She is such a fighter, everyone said she wont make it and will probably not lay eggs anyway why let her live. I say as long as she is eating well and trying I am not giving up on her. The only thing different this time is she is shaking her head some and the lack of cheeping.She does not have any signs of upper respiratory. She was vaccinated for mercks at the hatchery and when she was younger she was on medicated feed.Your hen sounds like mine so I suggest you continue giving her the baby vitamins and some electrolytes in her water. We put the vitamins in a little dish with a little of her feed moistened with the electrolytes(save a chick is what we used). This way we were sure she got them all. Anyone have any suggestions on cause and care I would love to hear from you all. I wish you the best.