1 week old chick has feather loss under 1 wing

I am the one who posted hatchling can't stand, her name is Esther, she has done well over the week, eating, drinking, leg improving daily but now she has lost her feathers on her left shoulder and down under her left wing. At first I thought it might be to pecking but I watch the 2 chicks for a half hour at a time and don't see pecking, also she is bald now in that spot. I went to the farm store and bought some stop pik and have applied that. Also I don't see any feathers in the brooder box. Any suggestions as to why this would occur and should I be concerned. She is on chick feed, has chick scratch, wood shavings in the box, plenty of space.