She was born in 1945 I think.
I will never forget the vivid description of the Rich Man in Jesus’ parable:
24 And he cried and said, Father Abraham, have mercy on me, and send Lazarus, that he may dip the tip of his finger in water, and cool my tongue; for I am tormented in this flame.
25 But Abraham said, Son, remember that thou in thy lifetime receivedst thy good things, and likewise Lazarus evil things: but now he is comforted, and thou art tormented.
26 And beside all this, between us and you there is a great gulf fixed: so that they which would pass from hence to you cannot; neither can they pass to us, that would come from thence. Luke 16: 24–26 KJV
Read the whole story at.
With such teachings from early childhood, the incentive to stick to it into death is enormous. One is taught rather to die a martyr’s death than to compromise the faith in God. Even though I deconverted from Christianity in midlife, I understand very well why your grandmother will not at her age. And I suggest you support her as a human being dear to you regardless of her beliefs. They comfort her and believing that heaven awaits after death does her no harm. She will not exist or be conscious after death to discover that she was wrong; she will experience no bitter disappointment.
The bitter disappointment would be to deconvert now in her old age and discover that she wasted her entire life in a deluded service to an imaginary friend in the sky. It may pain you to see her being deluded but I think it would pain you much more to see her suffer from disillusionment. It can leave people grappling for balance. If you take away one thing you have to give something else in its place. For an old mind to make this transition at someone else’s insistence is not good, in my opinion. You are young. Accept her as she is.