Has she ever had an echocardiogram to diagnose the nature of the heart murmur? It might help in figuring out if she would benefit from medication (which could possibly improve her heart function and make her a better candidate for surgery), as well as help the vets determine the best anesthetic protocol for her, if she does ever have to undergo general anesthesia.
"To close your eyes will not ease another's pain." ~ Chinese Proverb
“We must not refuse to see with our eyes what they must endure with their bodies.” ~ Gretchen Wyler