Give the vitamins some time. Injuries can also take time. If you should lose her, I would ask your state vet lab do a necropsy and testing for what was wrong. Keep food and water close to her. A chicken sling with food and water in front can sometimes help keep them nourished while recovering if they tolerate it. Here are some examples in post 5, 11-13:
https://www.backyardchickens.com/threads/versions-of-chick-chairs-please.1166308/
https://www.backyardchickens.com/threads/versions-of-chick-chairs-please.1166308/