rabbit died suddenly

I was quite upset to find my dear rabbit had died suddenly during the night this week, after appearing perfectly happy and normal the night before. She was abandoned as an adult over 5 years ago, so I don't know her age. She had had some health problems, including a sprained spinal cord when I found her, which responded well to steroids. Also chronic conjunctivitis and an ear abscess which I had treated five years ago. I have three cats as well. Any thoughts? She was my first rabbit.