Hi there, and thank you for your question. I am a licensed veterinarian and would be happy to assist you. If your dog is not on heartworm preventative, then I could consider parasites to be a possible cause for the diarrhea, and I would recommend you stop at a pet store and buy some over the counter dewormer and give a dose. If she is on monthly heartworm preventative, then parasites are less likely. In that case, I would try fiber supplementation. You can give 1 and 1/2 teaspoons of Metamucil mixed with her food twice daily. I would also try probiotics... ideally, a product formulated for dogs, and you can buy them at pet stores. A product like this would work:
Or you can try giving plain yogurt, 2 tablespoons twice daily. I would stop giving the Immodium, because you should not use it longer than 2 days. '
To recap, give dewormer, Metamucil, and probiotics or yogurt. Give it a week or so to see if signs resolve. Hope this helps... best of luck! Please feel free to reply before rating my service if you have further questions.