That's the problem when dying from COPD you are all there up to the end. It's an ugly death. I think your reasoning is quite sound and I'm in complete agreement.
I wonder if Heather knew in advance? Do you think that could explain her losing it as she has? There has to be more to that story. Her behavior is very odd.
It's definitely hard to explain her behavior since he died. Grieving manifests differently in different people, but we all pick up the pieces and move on with our lives. We have jobs to get back to, obligations to tend to, lives to lead. And we usually don't have longer than a week or two to do this. Yes, we are still grieving, but we carry on and grieve simultaneously. She seems to have completely shut down over this. It just makes you think, as I believe you have correctly stated, that there is more to the story here. Maybe she did know in advance. If that's the case, then it's more than grief with her, it's a lot of things. Hard to say. But yes, her behavior is very odd to say the least.
It could still be high drama on her part, wanting attention, but since the release of the autopsy report and now knowing the cause of death, and the distinct possibility that Art took matters into his own hands, it makes me wonder what Heather knew and when she knew it.