Why is everyone calling Yvonne stupid/an idiot? This system has forced her to do awful things, and the one time she refused it destroyed her entire family (when it prompted her to basically kill Elsa, no less). Then here, in a pivotal moment, it flashed a ton of literal warning signs. She has no idea what that could mean (and neither do we). I'd be scared shitless, too.
Because all she had to do was to communicate with Elsa on what's going on then see how she respond then this whole thing could've been avoided. I highly doubt Elsa would dismiss what Evie would claim if she had decided to spoken up about the whole system instead of bottling it up. The two would've probably tried to do something too by that point.
I honestly would've preferred for the story to go that route. I want to know the mechanic of the villainess system.