I agree, sort of... We don't know why she is living at home - whether she has lived on her own for a few years and has had to move back home for financial reasons, or she's lived with them all along because she chooses to. I'm 22, and I've lived on my own for two years, working through college so I can pay my own expenses and be independent. If I had to move back home for financial reasons, which many young people are having to do these days, I'd expect my parents to treat me like an adult because I've lived on my own for this long and I'm used to having adult priviledges. I would in turn do whatever I could to help out, not interfere w/their lives, and get myself into a good job as soon as possible. If they threw rules like that my way, I'd leave, if at all possible. Whether that means living w/friends, another relative, whatever - I wouldn't put up with that kind of treatment.
I believe that Dear Abby should have advised her to take the vacation and move out. Not "get married" or "bring a chaperone" (which in my mind = decline the vacation).