I am so sorry for your loss. It must have been the hardest ever to experience.
I have a five pound Yorkie and she has breathing issues. Last vet (I've tried a few to get help for this) I took her too was adamant that she doesn't have a tracheal problem but without any test at all. She never makes the breathing noises while at the vet that she makes at home. Awake and asleep.
Her episodes of breathing issues come and go and stress me out. Last time, at about three in the morning, it lasted for about thirty minutes.....longest ever. She cannot breathe, her tongue and gums get purple and sometimes her nose makes bubbles. She paces back and forth and seems to look to me for help and there is nothing I can think of to do to help her. I was so relieved when it was over.
I have tried to record it on my phone but it seems to distress her more when I am pointing the phone at her, so I stop.
Again, I am so sorry for your loss.