has she been treated for mites in the past? Skip is right it could be anything but I believe IBD she would have expired by mow a couple of moths is usually all it takes. Personally I'd look to accidental poisoning if there has been mites in her recent past. Poisoning is far too common, although there are about 1000 other possible culprits. A vet trip is needed, cultures and x-rays.
Is the other ball she shared with at the store sick it would have shown symptoms of IBD quickly it Royals it comes on fast.