I am so sorry your baby is experiencing these problems, and I am frustrated for you that all of the testing and exams have not determined the cause.
I haven't heard of a similar situation. Does she still have a swollen belly?
I found something on petMD -- just something to maybe consider, about narcolepsy and cataplexy:
Narcolepsy and Cataplexy in Dogs | petMD
The article does not indicate shortness of breath as a symptom, but it mentions that episodes can be triggered by moments of excitement, like eating.
Sounds like something neurological may be going on, and often these things cannot be explained. Do you have access to a neurologist?
Keep us posted.