Oh, I am so sorry, flemishwhite. So distressing for you and your wife.
Unfortunately, rabbits can have a seizure and even scream or make other vocalisations when they die. Even when euthanised.
This can occur with other animals and people also.
With people, the laboured breath and odd sounds (agonal respiration) is often associated with heart attack or stroke. It’s thought to be a brain stem reflex.
To truly know what caused her death, you’d need a necropsy done, I’m afraid.
It sounds as if there was little you could do for your girl at that point except love on her. I know how heartbreaking it is. One of my own passed suddenly when she was seemingly fine all day. I was in them with cleaning and she suddenly darted across the room and started fitting. It was all so sudden and fast.
I’m touched by the fact Snowy sought you and your wife out in her last moments. She must have trusted you both very much.
***Binky Free, Snowy***
Sending some gentle (((hugs))) for Cheyenne.