What is the day from her last tie? May be she is one that ovulaites (sp) late? Keep on loving her and watch her close (I am sure you already are). Can you feel the puppies moving? I hope that everything works out for you and her. I always try to think positive and look at the other good things going on. Has she been to the vet? Do you know how many to expect? If you are really worried that something is not right, call the vet and maybe bring her in. I hope everything is well. There are a lot of really experienced breeders on here that have really great advice.
I hope you are getting puppy kisses soon.