I am so disappointed that it is not her eyes because that would have been such an easy fix.
It sounds heart breaking for you seeing her like that and not knowing what to do to help her. If she is eating and drinking but struggling to get to the food then all I can suggest is that you hand feed her whenever you can and treat her with bits of special food like scrambled egg and yoghurt and scraps of meat and fish and mealy worms etc and just let her know you care.
I really don't know what else to suggest. It's hard when you have a pet that is unwell but they can't tell you what's wrong.
If she is not getting picked on by your other hens and she is eating and drinking and has been a bit "slow" like this for most of her life, then it maybe that she is quite happy in her own little way and just accepts that this is how life is. so try not to be too sad.
The important thing is to make sure she is safe (can't fall and get stuck somewhere or be attacked by predators or other hens) and has access to food and water. If she was in a lot of pain she would probably stop eating. The fact that she is still taking food is certainly a good sign.
Really hope this is just a passing phase and she picks up soon though or that someone else comes along with more experience of this ailment and how to treat it.
Sending hugs to you both
Barbara