I think it depends on the breed and the age to which they normally live. If she is a healthy dog of a breed that would normally live into their teens I would say have the op done, as these days the anaesthetics can be reversed very quickly. If she is one of the larger breeds that don't tend to live much older than she is now then I would say let her enjoy her days and don't put her through the treatment.
Sorry you find yourself in this situation, and I hope your resolve it soon, I am sure your vet would not advise the op if it was not going to help.