Holy fucking shit. Bruh. Just… goddamn. I’m pretty sure my parents would be over the moon if I was wanting to marry someone like that, regardless of intentions. Furthermore, it sounds like they’re clear on what her feelings are and things like that. It’s totally possible that he’s looking for an heir which is why her attraction to his wealth isn’t something he has a problem with (he’s already planning to give it to her and/or any children she might end up having). It’s also possible (as someone else pointed out) that it may be more kinky and saying she is marrying him for his wealth is an easier (or less awkward) explanation. Regardless, however, it sounds like it’s consensual.

I think the way I’d handle it is to voice my concerns just to make sure she’s thought of what might happen. When you do so, make sure she understands you’re not rejecting her, but trying to make sure she’s thought everything through; and that you need some reassurance yourself that she’ll be okay. Explain that you care about her and you don’t want anything bad to happen to her, and that’s why you’re so concerned. Then let her go and be there for her if things go south. Ultimately, she’s an adult and you can’t stop her from living her own life. At least it sounds like this path will ensure she (and any children she might have with him) will live a good life.

I’m actually kinda jealous lol.