Nobody will know untill you try Duragesic. But because it only makes one pass through the system and liver you don't have as much constipation with duragesic. The only med in the US aproved for cancer pain only is Aqtiq, Fenatnyl loli pops which are the strongest med available outside of a hospital where IV meds can be constantly infused. If she's home arrange hopsice care at home and the same IV meds can be used at home supervised by a hopice nurse. I don't know if I would ask for a specific med because you don't know if it is what she needs or how she wil react. THat's the docs job to find the right med andmanage her pain. If he doesn't do it, He may be opening himself up to litigation, and I would have no problem making that threat for my mom.

If you are in the US there have been oncologist prosecuted succesfully for allowing patients to suffer tremendous pain due to a fear of turning a dieing person into an addict? Who cares. Get tough, fire the doc if you have to, hire an attorney if you have to. But step in where your mum can't speak for herself. Talk to the medical director of the hospital or hospice or that docs practice. It's not up to you to find the right med, but it is the docs job to manage her pain.
Good luck, Dave