Has she been on medicated feed for the whole 17weeks?
It very well could be a disease like Marek's - but there is no cure for that, so I would offer her supportive care/vitamin therapy. I would start by giving her 1/2tablet human B-Complex daily and 400IU of Vitamin E daily for a week. Give her a treat of hard boiled or scrambled egg, this will help with the uptake of E.
If she is bullied, I would watch to make sure that she is eating/drinking well (check to see if she goes to bed with a full crop). Provide her with some places she can get away from the others-a perch in the run works good. Add an extra feed/water station, etc.
Here's a great article on Marek's
http://www.backyardchickens.com/a/the-great-big-giant-mareks-disease-faq
Since you are in NC, if you happen to lose her, sending the body to the State Lab would give you more information. There are 4 labs in NC - Fletcher, Elkin, Raleigh and Monroe.
http://www.ncagr.gov/vet/ncvdl/