So sorry that she is not responding to food or water. Water is most important right now. Can you get a little water with electrolytes or sugar into her beak with a dropper, syringe, or a spoon. Try mixing water into some tuna or canned cat food, scrambled bits of egg, and watery chick feed. The purring sound might be mucus in her throat, but hard to know. Is she warm enough? Tube feeding could be something you might want to try at some point if you are interested in learning how. Does she move her legs and wings? A chicken sling or chair might be something you could make to get her upright in front of food and water for parts of the day, then let her out to sleep and stretch. Here are pages of pictures of slings:
https://www.backyardchickens.com/threads/versions-of-chick-chairs-please.1166308/
https://www.backyardchickens.com/threads/versions-of-chick-chairs-please.1166308/
