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.
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.