Well, if the market so undervalues that stuff, the logical step would be to go buy other people’s beanie babies for cheap, before people realize how much they are actually worth. And then sell heaps of them for profit, once people come to ther senses.

That’s obviousl a very stupid idea, that you could pose to her, and let her argue why she doesn’t do that. Maybe it triggers a realization about how value is constructed.
But maybe it’s not worth the risk of her taking up on this very stupid idea.