I'm sorry to hear about your hen
Sadly, from the symptoms you describe -weight loss and walking like a duck, it sounds like she's having reproductive problems. If she has been laying eggs for the last couple of years after the lash egg, it would be worth feeling inside the vent for an egg and feeling of her abdomen for bloat/swelling or feeling of fluid.
Sometimes supportive care is all you can do if they are declining from reproductive issues-hydration and trying to encourage them to eat. Check the crop to see it's emptying overnight and monitor for lice/mites and worms.