I'm sorry for your loss.
Sometimes it can be just a case of "failure to thrive" or some type of genetic/developmental defect.
If you are having trouble with chicks from the flea market or auction you may want to ask the seller more questions such as vaccination details, bio-security, breeding...
Have you gently looked into the closed eye to see if she may have gotten a piece of bedding/dust in it? If so you can flush it with saline to see if that helps.
Otherwise, could be either neurological or genetic developmental problem or a vitamin deficiency.
Add some vitamins to her water if you...