One of my 3 hens seems to be acting depressed??? She's eating and drinking but stays on her own and not interested in scrabbing around and her tail isn't sticking up??? I'm very worried about my poorly Matilda indeed.
Sorry to hear about your girl. I would personally start with a thorough exam. Check her all over for parasites, injuries, bumble foot etc. if you are not sure what is normal or if something is off, look up pictures, post a pic on here or compare her to your other hens.