Hello, I'm Dr. Deb.
I recently came online and see that your question about Peanut hasn't been answered. I'm so sorry that you've had to wait for a response, but if you still need assistance, I'd like to help if I can.
This is obviously a very, very difficult situation since it sounds as if she's had the best care and been seen by highly experienced and educated veterinarians.
Her symptoms sound like they might be consistent with Inflammatory Bowel Disease although without multiple biopsies of her intestines, we wouldn't know for sure.
Most owners are understandably reluctant to put their dogs through such an invasive procedure, although the results can often be quite rewarding.
I'm assuming that testing has been done to rule out issues with her pancreas?
Also, I'm assuming that a gastrointestinal blood test to evaluate her folate and B-12 levels have been done?
Obviously, without a diagnosis, it's going to be difficult to know how to proceed in terms of treatment. I can speculate as to which drugs were tried and why but it might be helpful if I'm provided a list of them so ones which I might suggest haven't already been used.
I know how desperate your sister must be if Peanut has remained non-responsive to any of the drugs she's been given. As much as I hate to even mention it, I'd have to be worried that something fairly serious such as cancer might be the cause for her behavior
. Even though we typically see cancer in older dogs, unfortunately, younger ones develop it as well. This is another reason why a biopsy might be something to consider.
I hope this at least provides a few additional options to consider but, again, my apologies for the delayed reply. Deb