Advice needed on a badly beaten up chicken.

Looking for some advice on one of my chickens which has been badly beaten up by two others.
We got 6 chickens almost four years ago. Three from a supplier, and three rescue hens.
Over the years we have lost three with only one of the rescue hens remaining.
All three got on okay, with no squabbling.
Until yesterday.
When I went to feed them, the coop was covered in feathers, and I found our remaining rescue hen in a pretty bad way. My first thought was a fox had got in, but we don't have fox problems here.
Almost all her feathers on her neck and back are gone, and what is left is a mass of cuts and blood.
She is also just sitting in the nesting box, not moving to eat or drink.
I lifted her out and put her down at some grain, but she was immediately attacked by one of the other hens.
I have now separated them in the coop.
My neighbour says, put it 'out of it's misery', but he is a heartless sod!
Is there anything I can do to help her, and if so, and she doesn't improve, how long do I give her until I do have to follow my neighbours advice?
Our local vet, (for our dogs) is not 'hen friendly', and would probably agree with my neighbour.
Thanks

Peace and quiet is what she needs, I would make sure she is not stressed by seeing her attackers too.  As long as she is eating and drinking (give her some tonic/spice) then I wouldn't cull her.  Your problem is going to,be reintroducing her to the flock.  I don't think that will be possible, so re homing is your only option assuming she improves.

However, the real problem is the bullies, if they turn on other hens, I'd cull them!

Hens will spot signs of sickness or weakness in another hen long before humans will , they will also abandon or finish off weak offspring .

Chicken nature, they do not play by human rules!

Peace and quiet is what she needs, I would make sure she is not stressed by seeing her attackers too.  As long as she is eating and drinking (give her some tonic/spice) then I wouldn't cull her.  Your problem is going to,be reintroducing her to the flock.  I don't think that will be possible, so re homing is your only option assuming she improves.

However, the real problem is the bullies, if they turn on other hens, I'd cull them!

.  I agree with this post. It may just be one doing it. A few years ago one of my favourite characterful warrens was constantly picked on viciously by a bluebelle. As I tried to coax her out of the coop I would watch the bb peep round the side of the run looking for her. She would walk up looking the other way then attack. It was just like a spiteful bully in the playground. I kept the warren and gave the bb away, pleased in the knowledge that she in turn would be picked on.