I would worm her at least. It won’t hurt the others if you want to worm them. Valbazen is in a few feed stores, but more available online. SafeGuard is in most feed stores and TSC. Look her over for any possible mites or lice as well. What do her poops look like? Oyster shell works for calcium for eggs, but doesn’t help grind up food in the gizzard. Some get enough grit in the soil, but I always put some granite poultry grit out in the run in case they are not getting enough.