Hello, and thanks for writing in.
The shells can cause a foreign body obstruction in the intestines, and can be sharp enough to cause a lot of pain. I would recommend having X-rays taken of her to see how many shell pieces are visible, and where they are. I know veterinarians who live on the coasts who do exploratory surgeries to remove shell pieces that are stuck or causing problems while going through the intestines, especially if the symptoms continue after 24 hours of ingesting the shells. At home, you can try feeding bland food, such as boiled hamburger and rice or cooked chicken and rice. Pepto-Bismol can sometimes be used to soothe a dog's stomach, but I would not recommend using it in this case, especially if X-rays are going to be taken, because Pepto can give the false appearance of something abnormal in the digestive tract.
I hope this helps.