Hello, my name is Dr. Kara and I have over 20 years of experience as a veterinarian.
I am very sorry to hear that Nikkinoo isn't herself and I understand your concern for her given her tarry, black stools. That can indicate digested blood in her stools.
Dogs can sit abnormally when they have abdominal pain and if she has swelling of abdominal organs or pain in her abdomen that can put pressure on her diaphragm, which puts pressure on her chest cavity and may cause abnormal breathing. Given that we know she has abnormal stools I would concentrate on looking for an abnormality in her abdomen.
I see that she has had a course of antibiotics and anti-diarrheal medication as well as her anal glands being checked but what sort of diagnostics have been done?
Digested blood in her stools can be from gastrointestinal ulcers, which can be related to kidney or liver disease or pancreatitis, gastrointestinal parasites, or even a mass in her gastrointestinal tract.
I would recommend a complete blood count, biochemistry profile and a specific blood test for pancreatitis called Can Spec PL (canine specific pancreatic lipase) as well as a stool test for gastrointestinal parasites. A urinalysis may be helpful as well depending upon what her blood tests show.
If those tests are non-diagnostic then abdominal radiographs and an abdominal ultrasound may be helpful. This allows us to look at organ size and shape, the consistency of the organs as well as the thickness of the stomach wall and intestinal walls.
In the meantime to try and settle her stomach today you can try either:
1) Pepcid-ac (famotidine) at one half of a 10mg tablet per 10 to 20 pounds of body weight every 12 hours.
2) Prilosec (omeprazole) at one half of a 10mg tablet per 10 to 20 pounds of body weight every 24 hours.
These will reduce stomach acid and should help if this is related to primary gastrointestinal upset, nausea and gastrointestinal irritation.
I also recommend that you start a bland diet of 1/3 boiled hamburger (or white skinless chicken), all fats and juices drained off mixed with 2/3 boiled, plain white rice. While this isn't a balanced diet it is fine short term to see if a bland diet helps her feel better.
If this protocol helps you can give her the acid reducers long term and she can eat a prescription bland diet, either Hills i/d or Purina Veterinary Diets EN.
Best of luck with your girl, please let me know if you have any further questions.