I'm sorry if it sounded like I was saying that strokes don't affect people. I realize that they do...my grandfather had one and it definitely changed his personality, though luckily (I guess) it was the opposite. He was a mean man until the stroke, then became mellow as could be.
It just seemed like, in the context of this thread, a stroke was being used as a "well, that poor thing- of course she doesn't know any better than to believe in a God and talk to him. She wouldn't have believed him if it wasn't for that stroke" type comment than anything else, at least to me. Maybe I shouldn't have read it like that, but I did. Hard to know what the underlying purpose of a comment is without connotations I guess.
It could very well be that she didn't consider the waiter's feelings because of her stroke, because like you said, behavior does change. But you don't have to have a near fatality or brain alteration to believe in a God.