1. You get divorced and she keeps her money
2. As a couple, you never spend "her" money because it's "her" money. You die having spent none of the money
3. At some point in the future, you start spending "her" money
(3) doesn't make sense given she's uncomfortable with it now. (2) also doesn't make much sense. So to me it seems like either she's acting irrationally or expects that (1) is a strong possibility.
OP, it sounds like this would be a huge shift in thinking for both you and your wife, but I hope you can find your way there (maybe with the help of a marriage counselor).
These people should see a councelor and talk about why they think it's important to keep it separate in the first place.
That might be the case, but why couldn't it instead be that she thinks it's unlikely, but still possible (and therefore she needs to be prepared for it)? Like even if she thought there's a 5-10% chance, it doesn't seem irrational to prepare for it? (Note I'm not saying it's a good idea to do this, just saying it seems rational.)