I hate to say it, but that was my first thought too, Cathy.
Poor Sasha! And poor you, Sheri! Is your vet saying that this is from the surgery 6 years ago? If so, I might be tempted to take her to a specialist or if you have someone in your area who treats a lot of Cavaliers take her to him.
You say a small throat opening. I don't mean to sound dumb, but do you mean that her throat was actually opened because of the prolapse OR that her throat was too small for the tube that they used while they did the surgery?
You might also want to check and see if there is a holistic vet in your area. I've considered taking one of mine to try holistic medicine, and have still not ruled it out completely.
My gut says that it's time for another opinion - they call it Veterinary PRACTICE for a reason!
Good luck & keep us informed.
RIP Wallis, John Robert, Tibby & Pip
Mom to JoJo, Roxie & Linguini (Cavaliers)
and my birds Moji (Senegal) and Walter (Blue Front Amazon)