I would make sure the other chicks aren't bullying her and that she gets enough food and water. You could also try feeding her raw egg yolks so she could get all the nutrients she needs along with her regular feed. Wish you the best.
If she is behaving as a normal sized chick she should be fine. She will just be a smaller hen. If you notice anything wrong with her, I would keep her in a separate cage if you have other chicks.