My hen won't stand up.

Hi there, I have a 1 1/2 year old Isa Brown hen that has recently lost leg strength. She is currently lying in a carry cage on a towel with pellets and water at reach. She won't stand up at all but she is completely responsive, eats, drinks and pecks at my rabbit when she comes around so I know she is well enough to defend her self. Yesterday we were evacuated from my town because of a fire threat so we packed up all the animals and had them moved to my aunties farm. She was then put in a large chicken coop with only her sisters and my rabbit. No other threats around. She would have been very dehydrated during the car ride but she drunk plenty of water when she got out. It was a couple of hours after they had settled into their new coop that I noticed she had flopped onto her side and wasn't using her legs and still is now that we are home. And I honestly thought I would find her dead in the morning but instead she was trying to get out of her box to greet me but couldn't get her legs to work. What could be wrong with her and what can I do other then keep her fed and hydrated?

 

I couldn't find any lice but I did give her a warming treatment through her water. Her comb is bright and she seems to be improving e.g. She's able to swivel around now and fly down from her box but lands on her bottom. Still isn't walking though. She can find her water and the food I put near her so she can keep healthy but apart from that I heard that she may just be on her last legs due to the stress and may want to roll over and die. I'll keep her fed and watered until she decides she's had enough of life aha.