I had a Buff Orpington that had this condition for 24 hours after falling off a ramp the previous night (I was trying to assist her and it was a difficult reach for me). She flew/jumped and fell over- this was inside a coop and I just couldn't reach her properly.
The next morning the condition was there.
The hawks watched her all day and kept flying over. I hovered around her for hours that day, worried sick. Then the following day it was gone. She refused to eat or drink for 24 hours.
It was a complete recovery and I assume she had some sort of neck strain?
Edited to add: I was thinking this over and realized that it did take more like 48 hours for it to fully go away.
why will she be culled before you even try to treat her? I have been through one week treating a 3 - 4 month old chick Her neck was COMPLETELY floppy like it had been severed inside. I wrote in here, found out about wry neck, and started the vitamins on her. There were small but IMMEDIATE improvements from the very first dose! A week out she had full control of her neck but is still gaining balance issues in her legs. She's doing FANTASTIC and I expect her to be back to 100% in no time. I've read that some take as long as a couple of months to recover and others reccover quickly.
It is not cost effective to treat individuals, especially when a relatively large production flock is involved. Affected pullet is part of breeding program. If infirmities detected, then birds with infirmities will be culled. I do not know if there is a genetic component to this but suspect it is possible and genetic problems will over time be eliminated or at least controlled. In this case culling means her wing band number will be removed from list of potential breeders and I will be watching for occurence in her close kin. If condition is not communicable, then she will be allowed to growout but she still will not be part of breeding program.
Owing to rearing system involving quality free-range forage and supplement feed, I am inclined to doubt this is a nutritional problem. Mechanical cause is more plausible. Older males of program molest younger birds frequently and roost site for these guys is anywhere from 9 to 12 feet above ground. These guys are being selected for free range performance. Predators have not been a significant selection force owing to dog but the birds must be resistant to environmental conditions, local parasites and be able to fly up and into elevated roost that provides measure of protection from ground predators and great horned owls. This condition prevents flight making avoidance of weather and predators at night nearly impossible.
Most feeds do not have selenium in them. If your soil is deficient, they can free range all they want and not get enough. Unless you add free choice minerals, this condition may resurface repeatedly . It is not likely a genetic thing, it probably is a deficiency