I had a labrador puppy that did this.. . She was a very sick dog, we adopted her at a local pet store. She had hip problems, stomache problems, and kidney issues...I'm sure there were more. But, due to the extreme hip pain she had at only six months of age we put her down.. . I do hope you will take her to the vet and find out why she is doing this. It isn't normal for dogs to sleep in their own poop.. . It is more normal for them to sniff and eat it than to lay in it.