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...
Are you using B complex vitamins? That is best since they contain all B’s including riboflavin. Dosage is 1/4 to 1/2 tablet daily crushed into a little food or in a spoonful of water daily. Hopefully, it is not Mareks, but an injury or vitamin deficiency. Time will tell.