You definitely want to get your dog to the vet as soon as possible. However, here are a couple of common reasons that your dog may have this. One is a urinary tract infection UTI. Traces of blood will be found in the urine and she may urinate more frequently and may also strain while urinating. another reason might be bladder or kidney stones or crystals. These can pass through your dog and cause bloody urine and straining while going also. Blood work up can let you know but I would try for these two things first since they are both common in female dogs.