She could be constipated, or perhaps there is a blockage that you don't know about. Dogs can and will eat just about anything they find on the ground or floor. For instance, my mother's dog eats rocks, which cause blockages and have to be surgically removed. I would keep an eye on her, if she continues to eat and doesn't poop, you may have a problem.
I suggest calling your vet and describing it to them. They will be able to assess whether they need to see her or not. Always better to be safe.