She was doing very high-end modeling and she could have very well married any old man to secure retirement. She also has a jewelry business, so it isn't like she is going to sit around and do nothing. All successful people know retirement isn't an option, as death soon follows retirement. She married to increase her wealth no doubt, but this has always been done.
High-end modeling has a very short life span. Yes, she has a business, but marrying Donald insures that if her business slows down or fails, she has something to fall back on.
She can fall back on her butt. :) I recall one of the old doctors at the Military Enlistment Processing Office saying this years ago about a young man who wasn't there on time because of some school activity and the recruiter said "He needs something to fall back on." Then the doctor replied "He can fall back on his a$$." I know this is off subject but I tend to be that way. :)
From a psychological standpoint, women like a man with power. The more power, the more attraction. Zack is probably right, it is the money. If I had $10 billion net worth, I doubt I'd be single.