that was incredibly heartbreaking, Frances. I am so very sorry for your loss and can totally relate. Our Gandalf passed at 17 with pancreatitis, and after a stroke which left him unable to get around.
It sounds to me as if your sweetie had stroke that day. Surprised they did not figure that. When Gandalf had his stroke, his little front paw went limp and he was unable to move around.
You did the right thing by sending her over the rainbow bridge. The kindest gift you could give.
Thank you so much for sharing.