This story is a perfect example of the difficulty facing doctors when deciding what to prescribe. Many people with chronic illness function very well on traditional treatment. They are not pain-free but they are able to live and come to terms with the pain they have. A small percentage with exactly the same illness are unable or unwilling to do so. 
The problem with narcotics is that they work beautifully. It doesn't matter whether you have headaches, back pains or joint pains, narcotics will be better than anything you ever tried before. But it comes with huge costs. If you take it for life you WILL be addicted. Addiction is a physical change at cellular level in the body whereby normal metabolism requires the addictive substance. The writer may be doing well now, but she is addicted whether she believes it or not, and as tolerance develops, fentanyl will become less effective so increasing doses will be required, eventually to dangerous levels. This is why it shortens lives.