In some ways only your grandmother can answer this question. Pain relief often improves a patient's ability to move around and improves quality of life. It's hard to put a price tag on six months of improved health and increased function.
A recent study was done of patients over age 80 having surgery for spinal stenosis. Everyone got some pain relief. Many were pain free for the first time in months or years. They were able to stop taking pain medications.
This kind of improvement can actually preserve and prolong an older adult's life. Less pain means easier movement and less chance of injuries or falls. Even at age 82 your grandmother could have lived another 10 or more years. Without knowing when life will end, some say quality of life is the guiding factor in making these kinds of decisions.