We had the necropsy done this afternoon. She died of a ruptured liver. When the doc opened her up, he said she looked very healthy but when he got close to the liver, it was surrounded by a pool of blood. He told me that there was nothing I could have done to prevent it or to help her, so that made me feel better.
My DH and I wrapped her back up and went for a drive by the lake. We found a nice spot away from homes/busy roads and set her in her final resting place in the woods. That was a strange feeling for me but I feel good about the decision. I wanted to be sure there was no disease beforehand so that I wouldn't possibly be spreading something.
It feels very, very good to know what caused her death.