I don't think there were any errors here, and I didn't get the impression this was only evaluating errors.
I don't think her doctors missed anything that ought to have been caught. She seemed completely fine five minutes before she was irrecoverably dead (i.e., her heart muscle hadn't just stopped, but part of it had died).
And that's what confuses me about this rating system for evaluating what was and wasn't preventable. My best guess is that there truly wasn't anything anyone should have done, that it was just a freak thing that happened.
And I guess that's emotionally simpler. The grief isn't any less deep, but it's not complicated by anger. "Sometimes bad things just happen with no warning" sucks, but it's not complicated.
I suppose I do have a bias toward continuing to assume that's true in her case, for my own sake.
The above article is describing amenable medical errors. I don’t want to make assumptions about how your sister’s death would be classified.
However, I am so sorry for your loss, which is a tragedy. We need to do better, as this should not be happening.