I have had something like this happen to two chooks of mine.
With the first it was a nervous system disorder where one side of her body just went limp and there was nothing we could do.

With the other - I can't quite remember the condition but I do remember there was an option for treatment. I tried to give this bird a bit of time to recover as she was eating and drinking and alert, just couldn't move properly. I had to take her to bed and put her out and bring food/water to her. After 3 days of not getting better (but still fully alert and bright eyed) I took her to the vet. The option of treatment cost to much to justify, especially considering the chance of it working was not very good after not showing improvement for a few days. In the end we decided to euthanise.

I understand what you mean, they are more than 'just chooks' and it is a tough thing when any animal is sick. I definitely would take her to the vet to get an answer as it is too stressful for you and for your pet to have questions. Im sorry for the sombre news from my experience but hope your outcome is better than mine. FWIW, I received a call from my vet clinic later that afternoon about the death of the chook to check I was ok! Some people understand!