I'm so sorry for Bella's diagnosis
.
You are so on top of everything though, and your post was so informative too - it sounds like your vet is really on it as well. I have not been through this, so I don't have much to say about it - but are there any other antitussives she could try? Was stent surgery discussed or is now not the time for that?
I really wish you the best, and I know you'll get her through this - and with a good vet, you may be able to get her where she needs to be without further intervention. Keep us posted.