[ychook]

I found one of my old battery hens huddled in corner & thot dead but still alive. Brought indoors not really eating, still cold but has lasted overnight. Any advice on how to treat? Thanks

[joyfull]

perhaps she is about to lay a soft shelled egg, this does make them unwell as there is nothing for their muscles to push against. Keep an eye on her to see if she passes it whole and that it doesn't break inside her 

[EddTheDuck]

If it's still in the same state tomorrow, unfortunately there's only one thing to do....

[joyfull]

wrong - you don't need to cull just for that.
They usually take a day or so to pass a softee. Keep an eye on her rear end to make sure you cant see any goo hanging out of her vent otherwise the others will peck her rear and can lead to her being killed by them.

[Lindeggs]

Keep her warm, keep her in a quiet place with dim lighting, make sure she has food and water available and see how she goes...

If sitting huddled up and lost appetite are the only symptms, there are a lot of things that could be wrong with her.  Until she shows other symptoms there is no way of knowing whether it's something she will recover from or something more serious.