Thank you for the videos
Have you looked inside her ears just to make sure there is no infection, debris or ear mites?
Has she always flicked her head when eating? Does she only do that when eating crumbles or does she flick the head often.
The flicking of the head and loss of balance does sound neurological. Whether the cause is nutritional, genetic/developmental or disease (Marek's) related it would be hard to know.
Since she is stunted, I would lean toward genetics - but you can't rule out Marek's.
I would try Vitamin E (400IU daily) and 1/2 tablet human Vitamin B-Complex for a couple of weeks to see if that makes a difference. Give her a little treat of egg or tuna for Selenium, this helps with the uptake of E. Since you hand feed her/save goodies for her - egg with the vitamins mixed in would work nicely for "treat time".
I don't know of any natural de-wormers, can you tell us what that is? Getting a fecal float would be a good thing to do. If she has worms, then treating those with something like Safeguard or Valbazen is the way to go.
Her crop looks quite full in the video, which is a good thing if she's been eating, but I would also check it just to make sure it's emptying completely overnight.
Thank you
@Wyorp Rock for your time and attention on this. No, I haven't checked for ear mites, but will figure out how to this today for sure!!! Yikes... are ear mites contagious? None of my other girls have this 'tick' and I don't find mites or bugs on them. (I check everyone frequently).
Yes, she's always flicked her head to some degree when eating and even when not. I just went back through their "baby videos" and noticed it back then too, not quite as pronounced as it is now... but present for sure when eating & just standing.
When I first got the day old chicks - I REALLY wanted buff orpington chicks, but she was the last one left, so I took her. I had nothing then, to compare her to. I went back to the farm in May - and asked about the fact that she wasn't growing, and they said it's fine, Buff Orpington chicks are always "late bloomers". The were all vaccinated for Mareks... (so I was told.) Can Mareks come back?
Here is a video of Goldie - last May 2018 (not much growth since then) but here's the head shake just being held:
...
I always watch everyone's crop morning & night to make sure they're full at bedtime, and empty in the morning. Hers' seems to empty & fill nicely like the other girl's. She poops ok too - but I noticed her feet and legs - are always ICE cold... Granted it's winter weather here now (Jersey Shore) but the other girls' legs aren't that cold in comparison.
I think the vitamin E & B complex are an EXCELLANT idea, and would hurt at all, so I will definitely try this!!! Tuna for the Selenium is an excellent idea too! It will be easy to add that to her 'private' special treats! Awesome idea! Thank you!
The "natural wormers": I researched
a lot (like 2 years) before I began this wonderful journey with 'being owned by' chickens. My greatest fear was that I'd accidentally hurt one of the girls, due to my ignorance. I've also had horses for 25 years, so I'm familiar with medical stuffs, and versed in the worming process and it's important necessity. But for the chicks - since they're providing us with eggs... I really hesitated to introduce harsh, toxic chemicals. I am also one who (this sounds gross) but I examine their droppings carefully each day... and yes, a fecal float would definitely be a VERY good idea periodically! So here's a gross question... HOW do I do this? Put a poo - in a plastic baggie and take it into the vet? I've never done this... oof!
In my path of researching - I eventually landed on the "Fresh Eggs Daily" website - and her natural approach to worming, which is what I've been following. I actually make "smoothies" in my nutribullet for the chicks each month - using plain yogurt - and I include as much of the following as I can (what is growing in my gardens & can gather from foraging): fresh dill, carrots, cucumber, garlic, mint, nasturtium, plantain, pumpkin, dandelion greens, watermelon and squash. (most of which is also available at the market when it's out of season). These naturally diuretic plants - mixed in with plain yogurt, can flush any worms out of the host's body. Sometimes I add a drop of molasses.
Hope that helps?