[dugless]

We have a 5 year old ex battery hen she stopped luying 3 months ago.

two weeks ago she was ill with liquid poo and off her food,

she has rallied but now she is loosing a lot of her under feathers mainly from her back end

but now some off her body. is there anything we can do or will nature take its course.

[joyfull]

if there are no signs of any creepy crawlies (check the feather quills to see if any eggs or adults are on there also check around her vent) then she could be going through a moult.

[dugless]

Thank you, we were worried because she had been ill and she has never lost the amount

she is loosing in all the three and a half years we have had her.

[Beano]

We had a hen recover from an illness and then started losing feathers like you'd never believe. She would get up and leave a ring of feathers in her wake. I think it's as a result of having been ill (if you've checked for creepy crawlies and not found any).
It will be a shock to her as well, so give her some poultry spice in her food and some tonic in her water to help her through.  It sounds as if you're doing it anyway but keep an eye on her just in case there's  something more sinister going on.