Level 1 or 2 is considered acceptable by most pain management doctors and when it starts getting into the 3-5 range then you should start questioning whether the dose is strong enough.

Also another factor to consider is the amount of Morphine she is taking to maintain the pain threshold. If it is excessive oftentimes they will adjust the Fentanyl to a higher dose rate to reduce the morphine use. It's a balancing act. Most pain meds won't completely remove the pain - they merely move the pain threshold to an "acceptable" level.

Burning in the throat could be a side effect of radiation damage or also could be thrush, also caused by pH imbalance in the mouth, as a result of drymouth and/or radiation.