Bloody diarrhea is a serious concern.  Blood-tainted diarrhea can be a symptom of many things, including but not limited to bacterial or viral infections, foreign body, diet, parasites, disease and even stress. Diarrhea can be the sign of something very serious and can quickly lead to dehydration. For these reasons it is highly recommended that you take your dog to the veterinarian as soon as possible so that she can be accurately diagnosed and appropriately treated.