Seems borderline to me.
On the one hand, I think weddings are totally out of hand these days. Traveling all over the country for six months in preparation for a wedding is totally nuts. And she is putting some pretty strict demands on her bridesmaids. Telling them to set aside so much time and then telling them they're out of the wedding party if they're unable to make even just one party is unreasonable.
On the other hand, it's smart to be up front about this stuff. If she can afford a huge wedding and her friends can afford to do all this and want to, who am I to judge? Maybe this is a rich girl with rich friends and that's just the kind of stuff they do. And by telling everyone far in advance that things are going to be expensive, it gives them an out. However, I think if she can afford to splurge this much on her wedding, she ought to be willing to cover or at least help out with the expenses of the bridesmaids. I mean we're talking about multiple plane flights, hotel stays, probably ridiculously expensive dresses, etc. If you can afford a $50,000 wedding then you can afford to help your friends.
The biggest problem I foresee with this is that her bridesmaids, even though they were given ample warning that it will be time consuming and expensive, will not back out even if they want to. They'd feel too guilty about hurting the bride's feelings, instead going along with things, pretending everything's find, but letting the silent resentment build up until it leads to an explosion of drama.
The bride ought to have a 1-on-1 sit down with each and every bridesmaid to really drive home the kind of commitment this is and the expenses involved, and give each one a really big window of opportunity to back out now instead of waiting until the last minute.