I am sorry for your loss.
We had a dog that was diagnosed with AIHA when she was 2. In AIHA, the immune system attacks that dogs body, usually the red blood cells and the dog collapses. Usually the cause is not known, but our dog collapsed after having her immunizations. Although on Frontline at the time, she had developed an allergy to fleas. As a result, we watched immunizations and only gave her those required and tried to stagger them. We also were extremely flea vigilant. As a result, she lived until she was 10 and at that time, her immune system started attacking her spinal cord and we lost her.