Tricky one... it might be unromantic but I can see her point about the money. It's the person who bought most assets to the marriage who loses in the event of divorce.
I own a property but my DP doesn't. If we married then it didn't work out and we divorced he'd potentially be entitled to half my flat. I worked hard for it and made sacrifices to get on the property ladder so I wouldn't be happy to risk that. No that he's proposing but I think I'd say no. I'd also have issues about one man giving me to another at a wedding and me changing my name. I'm not a campaigning feminist or whatever but I am me, not a possession and not up for changing my identity. All this doesn't mean I don't love him.
But then, we're not having kids and that changes everything. If I was younger and planning DC I'd think differently.
Sharing finances while married is one thing, sharing them post marriage is another.... I'm not sure the lower earner/owner demanding marriage or leaving is particularly romantic either. What have they got to lose?