Not defective but maybe deceptive. Did the seller say the charm was included? Or did the pic show it on there? Coach is not responsible for the fob. Some actually get stolen or lost off the bags. Whether or not the seller mentioned this is another story. Seller may not have know it was missing. It is always the buyers job to ask questions though.
Definately not defective. It either was missing when she bought it or she removed it. It's a good idea to carefully check auction pics for those things because unless it was shown in the pic or specifically mentioned in the listing, she really did nothing wrong.
Look on the original listing and see if the pom pom was photographed and/or mentioned in the listing. If not, the seller did nothing wrong. If so, you could claim a SNAD with the seller. However, since she did mention Dillards does not sell this with the pom pom-which isn't true-she may have kept the pom pom, sold it in another auction, or never received it in the first place.
Unless you really know the style bag your getting and what's included, who would know that this charm is part of the deal? I usually give the seller the benefit of the doubt and do NOT think she was deceptive. Perhaps she honestly did not know this charm came with the bag.