Poor girl"Sling-Girl" seems to have developed this yellow crust on her right eye only. She keeps both eyes closed for the most part. Not sure what that indicates.
Thoughts on these?

Not sure what's going on there. Does she seem able to see - how her aim at food?
May be due to that's she's not active and able to move about preening, dust bathing, doing chicken things. I'm sure skin deteriorates over time if immobile like that, even around the eyes.
You can try wiping out with saline and applying an eye ointment to the eye to see if that helps.
I'm sorry that she's not improving, it must be sort of a miserable existence for her.