Layer feed has too much (4X) the calcium for non-laying pullets or chicks. It can damage kidneys. At this age also, she could be showing signs of possible coccidiosis. Amprollium or coxoid can be purchased for treatment if you think she has coccidiosis. Other sysmptoms are weakness, lethargy, not eating, and runny droppings, sometimes but not always with blood.
Is there anyway to get an all flock or flock raiser feed? Chick starter grower is also good for all chickens, as long as you put out crushed oyster shell for layers to take freely.
I would try to get the chicken to drink some fluids with electrolytes, perhaps offer water food or cooked egg. Is the chick moving the legs okay?
