She could have a broken leg or internal injuries. I would try to get her to eat on her own by holding a small scoop with watery chick feed and cooked egg up to her beak, and dipping her beak into water. A chick chair or sling might be a good way to get her up, but only do that if she is able to tolerate it. You might be able to make her a little nest to hold her up. Look at these links for homemade chick slings and see post 31 for the nest idea:
https://www.backyardchickens.com/threads/versions-of-chick-chairs-please.1166308/
https://www.backyardchickens.com/threads/versions-of-chick-chairs-please.1166308/