It's sounds like your dog is grieving or under some sort of distress. It would be a good idea to take a visit to the veterinarian's.
How old is your dog? Was this her first litter? If not, how many other litters has she had? Were the pups born healthy? Did you tell your vet that her only pup was born dead? She may need some kind of assistance after delivering a dead pup. She is 2 years old... I don't think her age matters when it comes to the toy she has chosen to carry around with her. She obviously needs the toy to help her through her loss. DO NOT take it away from her. It does NO harm & could do a lot of good for her. I don't see why you feel it is a problem. The toy can't hurt anything. Let her have it as long as she needs it! No matter how long! To take it away would be cruel to her. Let her deal with it "her" way, not yours! And tell your vet about the dead pup!! It could save her life next time... God bless her heart!