In my Grandmothers situation jamming a feeding tube in her would have been extreme and taking heroic efforts. At 100 years old this would not be right ... in the situation of Terri, yes a feeding tube is proper. She wasn’t winding down and no terminal illness. There was no reason to murder her. None.
“The fact that God can, and does, do what He wants is no guide for us humans when it comes to making decisions, because He reveals nothing to us about particular situations. We have only the data of reason and the data of Revelation to enlighten us. It is undoubtedly true that God takes people when He wants. But we have no knowledge of when that is until it happens, and so, obviously, that particular datum cannot possibly figure in the decision-making process.”
We are under an obligation to support life but ultimately whether we put a feeding tube in someone or not,we aren’t making the final call. We don’t know His mind so we just have to do the best we can but murder as in Terri’s situation was wrong.
I wouldn’t second-guess your grandmother’s decision, since she would know how distressful the procedure would have been. And a person’s age is not irrelevant.