"Changing [chemotherapy] treatment was the cause [of her death]" is a bit of a stretch.
I realize you're just paraphrasing the article, but I think it's a silly assertion for the author to make. She goes on to say:
The questions about what happened with Doherty’s cancer treatment are small things to consider in the grand scheme of a life. But they are the ones I’m preoccupied by today. Because Shannen Doherty didn’t expect to die.
Shannen Doherty might not have expected to die right away, but deep down she'd have to have known it would be sooner rather than later. She was first diagnosed almost ten years ago, and was diagnosed with Stage 4 metastasis almost five years ago. From a cursory googling, Stage 4 breast cancer has a five-year survival rate of 30% (
link), so frankly she was on borrowed time. The idea that "cancer treatment caused her to take a turn for the worse" is specious at best; I'm sure the doctors changed the treatment plan
precisely because the previous treatment wasn't working anymore...
EDIT: This is a crude analogy, but it reminds me of the old mechanic's tale that one should
not change automatic transmission fluid in a transmission that hasn't had a fluid change in a long time, because the new fluid will precipitate the deterioration of the transmission (more aggressive detergents, blah blah blah). It's total and complete
nonsense, but it has currency because people think "well it was still working until I got the fluid changed, and then-and-only-then did it crap out!" It's just coincidence though, not causation: the transmission was well on its way to failing in the first place, the fluid change did nothing to precipitate it.