How low is the potassium? Have they tried bringing the levels up? If you do a search on 'low potassium paralysis' you'll get some hits on articles about a low potassium condition in humans that causes paralysis with few other initial symptoms...it's usually reversible if the patient manages their potassium levels carefully, but if the levels fall too low they lose diaphragm (breathing) function. The condition is apparently genetic. Not sure if there's something like that in dogs or not
Is the food she switched to after the pancreatitis lower in potassium, higher in carbs, or higher in salt than the first food she was on? Just a thought....