Don't know what to tell you, it's a hard call.
JMO--Quality of life has always been an important issue for me in determining the decision to let go! It's never an easy decision and only one YOU can make it. Is she suffering, is she happy, is she pain free, will meds only delay the eventual and not really change her quality of life; all questions that only you know the answers to. Wish you the best and sorry you have such a serious and sad situation to deal with.