It sounds like her kidney disease has already been occuring. And, yes it is possible for them to show an increase in the severity of signs very quickly:( I think it would be a good idea to head to the ER, considering that she has a history of azotemia (increase kidney values), currently on Benazepril, and vomiting and diarrhea. Best case scenario, this is a bug or virus that is causing this (hopefully not the kidney disease). But, even with something like a virus or bug, this can be very serious in a dog with kidneys that are not working correctly b/c it can dehydrate the kidneys even further, and cause them more damage. If this were my case, I would hospitalize your dog and run a few tests, get your dog on some IV fluids and meds to stop the vomiting and diarrhea.

I hope this helps and wish you the best.
Dr. H