We've had bad luck with chicks bought from Tractor Supply. 6 out of 7 chickens purchased at TSC are already dead due to Marek's disease. One is still alive, but she has cancer due to Marek's disease. They were fine for the 1st 2 years, and in the 3rd year started getting sick. It's a minor miracle that our lone survivor is still alive, but she is living with a huge tumor, and needs fluid drained every 2-3 weeks.
I wouldn't buy any chicks from TSC due to their quality control problems with regards to vaccinating chickens for Marek's.
It's cost us literally thousands to treat all our sick chickens. Chicks purchased elsewhere haven't had as many issues as TSC chicks. I told TSC about this, and they offered to refund our purchase for these chicks.
If you can find a good vet with experience with chickens, I would take her there to get her diagnosed properly.