The answer to the anger is simple: she's SCARED, possibly scared out of her wits, because she's been presented with someone who completely violates her model that she was taught from childhood regarding how the world works. Further, because he denies her belief, he is moving out of her control. She can no longer use the carrot and stick of heaven and hell to keep him in line.
Worst of all, this adds a pernicious little seed to her mind: that maybe - MAYBE - he MIGHT just be RIGHT. Make no mistake about it: we scare believers ... sometimes A LOT.
[wry chuckle] I don't know as I looked all that deeply, Andrea. The fact is that a lot of christians, especially the evangelical variety, are scared to begin with. They're scared about going to hell, scared about pleasing their god, scared whether or not they're doing what they're supposed to be doing ... because of this ridiculous stricture they've involved themselves in.
And when such people are confronted with true freedom, they become like some animals who have been raised in cages: confronted with an open door to that cage, they're afraid to leave. The cage has become their known quantity, and the Great Unknown outside of that cage frightens them.
This is the legacy of indoctrination which religion leaves to us.
That's understandable since Christianity tells us we'll all meet again in the afterlife...if we've met certain (difficult to ascertain) criteria.
But the fact is that you don't really need religion to believe there could be an afterlife, do you? We tend to use religion to explain everything we don't understand...until we finally understand it. Why not...ghosts, too? Suppose they actually _do_ exist and they represent the souls of the departed? Maybe under specific circumstances the living can come into contact with them and we explain what we see as ghosts.
The cool thing is that if an afterlife _is_ possible, then maybe, especially if we plan for it beforehand, we actually can hook back up with those who left before us.
I have zero evidence for any of this and wouldn't even say I believe it is true. But it doesn't hurt to tell those I love that if we do come back in any meaningful way that we should try to go to an arranged time/place periodically until we finally meet again. All I get is another of those patiently knowing "oh, here's another of his kooky ideas" stares that are so familiar to me. But who cares? Better to plan ahead for something that may never occur than not to plan for something that just possibly could.
Your poor mom. That is very sad that she misses your dad so much. I know a little bit about how missing someone can make it seem like you're keeping their memory alive sort of. Well, at least it means they must have had one of those one-in-a-million relationships. She's very lucky from that perspective.
I wonder if she knows her video is all over the internets...if so I bet she'll ground him again!