Oh, don't you love it!!! Like Dr. Cheng said, can be many reasons. I've heard adding pineapple can deter them from eating poopsicles too.
There are many causes for a dog to ingest her own feces. Common causes may include inadequate digestive enzymes and/or decreased beneficial flora in the gut, or gastrointestinal parasites. However, some dogs simply like the taste.
Ask your vet if a broad spectrum medication, such as Drontal Plus for GI parasites would help.
You could also try giving her a probiotic such as Culturelle or Align, which are available over the counter. Begin with 1/4 of an adult human dose and gradually increase to a whole human dose. If she gets a loose stool drop her back down. Beneficial change to the gut flora takes 4 to 6 weeks, so don't get discouraged.
If she has acquired a taste for her feces you can sprinkle her dog food with Accent or other meat tenderizer for a few days. Meat tenderizer imparts an unpleasant taste to the feces. Alternatively or simultaneously, you could sprinkle her feces with red hot chili pepper sauce or other taste deterrent for a several days. This may have to be repeated occasionally.