Were all the eggs part of the same hatch?Everything else seems fine, shes just growing slower then the rest. I dont recall any exposed yolk sac, however, let me throw this idea out there. The black Lorps were collected from two of our hens, our hen hazel's chicks hatch no problem and are doing great. However Ethals eggs did not do so well, this one was the only one that lived all the other chicks died shortly after hatching. I never really considered this till now.
It does sound suspect, regardless, if Ethals eggs didn't develop and this is the only chick to make it from Ethals eggs.