P's family were in exactly the same position two weeks ago.
His 72 year old uncle had cancer and his heart medication (he had a heart condition too) wasn't working, he had one bad turn and the family (his wife and four grown up children) had to make that decision. They did. He died in hospital but they brought him home for three nights and had a very Irish wake. They all felt it was the right thing to do rather than to put his body through unnatural things. It made his death so much easier for them to deal with and his funeral really was a celebration of his life.
Your aunt is very strong to make the decision but it is one she will definitely not regret.