Sick Hen, Need Suggestions

Above is a link to a YouTube video of the hen. This came on sudenly. When I pick her up she rolls her head from side to side similarly to a blind person. She also spasms and throws her head against her back. She is unable to stand or hold herself level. If there is an indentation in the ground she pushes her head in and then her body rolls on one side. On level ground, she lays on one side and sometimes fights or spasms stretching her legs and wings. While lying on her side, she holds her head either tucked under her breast or stretched out forward. She exhibited an odd biting behavior snapping at the air as though for a flying insect. She did not show any respiratory distress or runny nose or eyes earlier, but as her condition worsens her breathing has become heavier and faster and I’m beginning to hear a little fluid build-up in her throat. I know she is dying, but would like to know the cause in hopes of preventing the rest of the flock from becoming infected. Is this a symptom of parasites? Is this a symptom of a common disease? Her coloca area is clean. She is offered a free choice a diet of a balanced 16% Organic layer ration and free access to the outdoors all day. The only toxic plant in the area I’m aware of is nightshade. There are mice that come into the chicken house at night. Her water is changed daily, but frequently it is dirty with poop when I come to clean it.

Haven't fgured ou how to post more than ne photo at a time...
Fat color is yellow--probably normal for pastured bird. If it is too bright and indicates liver distress, let me know.

gizzard?

craw contents

I am so sad no one replied to this thread at your time of need. Not only because you needed feedback and support, but also because I have been contemplating planting Four O'Clocks and have been searching and searching to find someone who could say just what you asked, if anyone had observed how a chicken reacts after having eaten the seeds. I did find a site where a woman said that her chickens and the birds love eating them, but she didn't indicate that there was a subsequent problem. It seems there is such conflicting information available.