Make sure that she is drinking fluids, and add SaveAChick electrolytes to them. Pedialyte, Gatorade, or sugar water can be used instead, until you get them. Check her crop in her upper right chest under the neck to make sure it has some food in it, but is not hard and impacted. Check to make sure that her vent is not blocked with droppings. Is she in a brooder with other chicks the same age?
I would make sure they are drinking well, and are alert and active. Bantams are more delicate chicks at first, and all chicks can suffer from stress when they are shipped to homes and feed stores. Sorry for your loss.
I have a chick 6 day's old. And she is on her back this morning.First time for me with chicks. Her brother is very strong but l thought she was too. Could the brother of hurt her in anyway? Have another chick coming out today. 2 still with the mother's but they've left all other's and not looked after them. Lost 3 maybe 4 now