She needs to be checked by a vet. Are there any new cats outside that are causing her to be nervous? Besides missing Smokey, are there any other changes in the house? New furniture, new people, new carpet? Have you changed the type of kitty litter you are using or new kind of food?
Does she have any fur mats or perhaps it is internal furballs? Be prepared, if you bring another adult cat into the house, it may not work out. Make sure the Cat Rescue folks will take the cat back if your cat wont accept a new one. Bringing a younger cat into the house might work better than another adult cat.
Good luck and hope she comes out of her funk soon.