Sorry about your weak chick. Was she shipped to you or from a feed store? Do you have Poultry NutriDrench to give a couple of drops orally, or electrolytes in your water? Keep her warm, and try to dip her water as often as possible. Check her bottom for stuck droppings and keep her vent clean. Shipping stress can be hard on a weaker chick. The smaller ones are especially delicate at first. Offer her some raw egg yolk with a dropper to see of she perks up.