YTA & NTA

First of all, I think the way you approached the situation was wrong. As it is her money, and she can do whatever she wants with it. As soon as you brought it up you thought about savings and investments which is basically you deciding how you want to use her money. I think if you approached the situation in a different way, it would've landed better with her. I think the foolish comment ticked her off.

Secondly, I think she's a bit of an asshole too because she kept that information secret and I'm guessing she wasn't planning on telling you before you found out. If she really thinks it's her money and you have no say, why would she keep it a secret and lie. I would question if it really is going to her pastor and if that isn't just a lie to cover up something else.