old english game hen is lethargic and not well Help

[BCbirder]

I got this hen in the spring and they guessed that she was three.She was always very chatty and alert bird, always checking out what I am up to and seeing if there is a treat. She seemed a bit quieter lately, but I thought it was because it has been raining and she has been inside the coop.
She is not as interested in eating, I offered her some boiled egg and bread and she ate a tiny bit but not like she would before, she would always , take big bites. She seems to be wanting to just sit, she walked a bit unsteady but not consistently unsteady, she walks a few steps was a bit tippy and then walked again, but so slowly. She had a poop and it was maybe a bit runny but not overly, it had the white and green colour and a bit watery but held it's form as a blob not a splat, (this is harder to explain than I thought) Her comb is red and normal looking, her feathers are fine and she has no sign of parasites, She is clean and has no poop at her vent. She is not wheezy or making any sort of sound like she is having difficulty breathing. She was shaking her head a bit when I was watching her the other night but she is not doing it now and I have her in a basket in the house this morning.
She hatched some chicks and raised them over the summer and I have not seen her in the nesting box but there were eggs in there. No eggs recently Not for at least two weeks for sure. There are three other hens in the pen with her and a rooster. None of the other hens are laying right now either so I didn't think much of that. She does not feel like she has lost weight, but she is so small already maybe 1 lb. She had legs mites when I got her and I soaked her feet in epsom salts a few times when I first got her. I looked at her legs and they still seem to have lifted scales so I gave her another treatment this morning but that doesn't seem to be the problem.
Her coop is an old sauna, with a old linoleum floor that I put shavings in for bedding. I have put shavings from a mill that were a mix of wood but recently I put in white pine shavings.

I would like to treat her myself but I don't know what I should do first. I have Ivermec and could give her some for worms? I have powder antibiotic but I don't want to give her anything that she doesn't need.
Mostly the signs are that she seems to sit quietly which is not her usual and she almost seems to be be squatting, I squeezed around and she doesn't seem to be egg bound, can't feel anything , not sure what egg bound feels like but she feels normal, not swollen or hard, or sensitive.
THis is one of my favourite hens, if anyone has any ideas of what might be wrong with her I would really appreciate it.

 

[BCbirder]

I forgot to say what she usually eats. I give her whole earth lay mash , I mix it with a bit of warm water in the morning. She prefers hen scratch, mix of cracked cron, wheat and oats. She has been foraging around with the other hens but recently has been in her pen which is mostly dirt. She gets kale and apples from the garden thrown in her pen. She is sitting quietly, just had another poop, this one was white and watery, maybe a bit foamy.