Did she actually eat the cob itself? It won't digest if she did and can cause a potentially fatal blockage.
Corn on the cob: This is not a toxic product. Corn kernels are a commonly-recommended ingredient in homemade diets. However, if swallowed whole on the cob, it is the right size and shape to block an intestine. This will initially seem like your dog is constipated dog with abdominal pain. However it can become serious if not cleared, as it can damage the intestine wall. Food backing up behind the blockage will do more damage to the intestine and can lead to perforation and a very sick dog. Surgical intervention is generally required to remove corn cobs. Toxic foods for dogs and cats | Pet Shed Community
Corn Cobs
Many dogs have suffered and, in some cases, died after eating corn-on-the-cob, when the corn cob caused partial or complete intestinal obstruction. Never allow your dog access to corn cobs. American Dog Trainers Network -- Safety Tips for Dogs -- Holiday & Seasonal Hazards Homemade Dog Food Dangers: Table Foods That Harm Dogs | Suite101.com