Most Helpful Guy
She's 18, she can do as she likes, parents should say ok but we're cutting you off. That's it, gotta move out and don't expect any help. Also convince her that he needs to sign a prenup...
Most Helpful Girl
How do you know this is a mental illness? She may just be childish. Just because someone acts differently than you do doesn't mean they are retarded. She is 18, a legal adult. Let her figure out her own life now instead of trying to control her. She will learn through her mistakes, but you have to let her make them first. I can see where she's coming from, but seeing as your "family is very respected and prestigious and rich" you're probably too self-centred to understand. 😁 Grow up, and let her find her own happiness, rather than telling her who she can and can't love.