Unfortunately, it doesn't look good for your Little Bit. Some chicks have what is classified as failure to thrive. It starts off with them seeming to sleep a bit more than the others and overall less activity than their peers. Then you start to see a size disparity, followed by poor feathering. This is usually because there is some hidden defect or problem incompatible with life. These chicks often die despite all you do to save them.
I would make sure that Little Bit is getting access to feed and water. Maybe set up a couple of feed stations in the space where they currently are to ensure that s/he is not getting bullied away from the resources. I would also add some vitamins to their water. It can't hurt and maybe will help her to build up some resistance to whatever is ailing her.
Do they have access to to the ground? And are they on medicated feed? I doubt they have cocci, but if they are on the ground that is always a possibility. A small, weak chick would be more prone to the effects of cocci than its larger, heartier peers.