I get this, and it's definitely an important lesson! But I also think degree of preference matters. - If your brother loves chocolate cake, but you like vanilla better, he should of course have chocolate for his birthday, and you should be gracious. But if your brother simply prefers chocolate, and you're allergic to it, he should be the gracious one and pick one of the five other flavors he likes almost as much.
Exactly. If he'd never been and it was always his dream, I would say she should go. But he's been before, and she had a bad experience last time, so he shouldn't make her go again.
It's all about how important the thing is to each party. The edge goes where it matters more - and in this case, I expect she has a stronger reason for not going than he has for going. She'd lose more then he'd gain.