Does this look like the normal bald spot when growing feathers? I only see it on the tiny one. In the last picture, you can see how much smaller she is than the other sex link. She eats a lot and is very active. I also don't see the others picking at her.
It looks normal to me like she is loosing her down so feathers can grow in. I would check to see what you are feeding them and what environment they are in if they are pecking each other since chicks don't really have a pecking order and aren't doing it on purpose to assert their dominance. I would just expand their area so they are not confined or raise their protein levels if ever necessary.
They are eating Helen's Best chick starter mash. She was eating some oatmeal in the pictures. They have only had that twice, as a treat. They were is a large dog crate and are in the living room. At 2 weeks, I built them a 5' x 2.5' box because I thought they need more space. I just added a window because they seemed to be more startled when they couldn't see. I also added some roosts and make sure they get fresh food and water every day.
I'll keep watching her closely to see if she gets any sores or if I can catch any of the others picking on her.