I don't think there is anything you can do for her, but I would not be surprised if she passes.
I have had chickens for years. I have found that for me, chicks might die about day 3 after hatching or at about 8 weeks.
The first, is called failure to thrive, and is usually a genetic problem and they pass after they no longer live on the yolk, but while not near as often, I have had enough that it is worth mentioning, some fail to thrive at about 8 weeks, give or take. I have always assumed that they had an ailment, that when the body was small, the needs were met, but as the body grew, it outgrew some internal organ, such as the heart or something.
I am just guessing, but I do not think it is contagious, but that behavior is not right for a chicken, something is wrong.
Mrs K