You will have to understand that your grandmother probably never got a chance to think for herself. Taking that into account, you should be gentle with her and don't make a big deal out of religion.
I apologize for my bluntness, but your grandma will die in ignorance, regardless if you tell her or not. You can probably save an old woman the emotional strife of thinking her grandson to be that evil atheist she projects in her mind. Old people are filled with pride and think younger people are just immature. While this might be true sometimes, it would be wiser for you to avoid such discussions because even if you properly expressed yourself, she would only hear "atheist".
Think about it, does it compensate to educate an old person?
I apologize for my bluntness, but your grandma will die in ignorance, regardless if you tell her or not. You can probably save an old woman the emotional strife of thinking her grandson to be that evil atheist she projects in her mind. Old people are filled with pride and think younger people are just immature. While this might be true sometimes, it would be wiser for you to avoid such discussions because even if you properly expressed yourself, she would only hear "atheist".
Think about it, does it compensate to educate an old person?