This is very common in cats, and less so in dogs. It's generally thought to be a behavior in a dog that was weaned to early - your dog was likely bred by a back yard breeder who's prime motive was to get the pups out of there as quickly as possible, and she probably didn't have enough time with her mom and siblings. Why you suddenly see this is another story. It's a 'self comforting' behavior, and it can come on at times of stress or illness. Think hard about if something in her life has changed, and keep an eye on her to make sure here aren't any other changes indicating a health issue. But if nothing shows up - well, then maybe sometimes she just needs more reassurance, and as long as she's not eating the blanket material, don't worry about it.