Dee Dee, I am so sorry to hear about Hallie. I am contacting others that have more experience with Cav. and hope to hear more. I shot a Cavalier show a number of years ago, thinking it might me a small breed for me. They had a cardiac vet speaking since heart disease is of major concern. This problem is new to me. I see you have been communicating with them on their site, so hopefully you will learn more.
I am told that a friend of mine who has a Cav. has this problem and works for a vet. I will check with her. She was to be her obedience dog and is now a lap dog. I am sure that would be okay with you.
Have you found more information on Doxie sites?

Remember that your fretting can go right through to Hallie so try not to worry. I know that is like saying don't think of rabbits but for your health too, try not to put too much stress on the two of you.
I know she is your life and she is yours. My prayers are with you for help.