Is it possible the others are bullying her and she doesn't get enough to eat? Or she could just be stunted somehow and slower to develop. I had one like that early this year. Had a hard time hatching and then had curled toes. I got his toes straightened out, but he developed WAY slower than his sibs. He survived though, and eventually did catch up to them. You said you brought her inside. Try giving her some special treats to give her a boost. Try feeding her some mashed up hard boiled egg yolk and put some kind of vitamins in her water (such as polyvisol without iron, poultry nutridrench, sav-a-chick vitamins, etc.). See if it seems to pep her up any.