[Ellie May]

I really have no idea but some thoughts.

Congestive heart failure can be associated with panting, especially at night. I don't want you to freak out but I would absolutely get a chest xray immediately if your vet didn't already do one. This would make sense with the "off" sound in her chest.

Has she ever had a complete thyroid panel and not just a T4?
Maybe she is having a temperature regulation issue related to her thyroid?

I don't see any real reason to "not" express the anal glands once just to see. I highlllllllly doubt that this is the issue and I do agree that once you start, you may not be able to stop, but doing it once may not be a big deal. A vet tech should be able to do it for about $10. You would be taking that chance though of it needing to be done regularly. If you are feeling brave you can feel them yourself to see if they are enlarged. They are at about 4 o'clock and 8 o'clock. Of course just because they aren't enlarged doesn't mean there isn't an issue but it can give you a pretty good idea.