Hi quick and final update. My hen has been in the hospital sling in my room for just over a week and has been getting regular tube fluids, soft force feeds, antibiotics and electrolytes and vitamins, plus rest and love. Sadly, her symptoms haven’t improved. Her legs and body are not gaining strength, she can move her neck and head and look around but she won’t peck or drink. I’m honestly not sure what has taken her, I really don’t think it was coryza as the symptoms were very different and the sulfa didn’t work for her (after 5 days I put her on a course of oxytetracycline but that didn’t help her either.) I suspect whatever disease it is has caused some neuro damage, sometimes her head movements have looked small seizures. I did give her vitamins for that but no change.
We’ve all said our goodbyes, the kids are forlorn (we raised her from a day old, she was only 7 months old and never even laid one of her long awaited blue eggs) but they accept that she’s not going to regain strength despite our best efforts. Lady Featherflower is going to the vet to be helped off to the big sleep tomorrow morning. Our other little silver pencilled Hamburg with the severely impacted crop is going in for euthanasia this week too

although she gets another day or two in the garden as she still seems happy doing her chicken business outside (pics below are from today)
Thanks so much to
@Wyorp Rock and those who walked me through the problem solving and treatments with both girls.