Probably a separate issue. A chicken can fight off a lot of things but when one thing gets them down other pathogens and parasites are opportunistic and get a foothold as well.
I dust the roosts with food grade DE. I don't think vinegar will do much for parasites.
Unless there is something...
You'll definitely need to address the lice/mites or whatever the parasite is. I recommend 5% Sevin dust as a starting point but at least you put something on her. If she has them, all your birds most likely have them as does all the bedding. I would clean out all the bedding in the building...