My fiancé’s sister isn’t going to make the effort to come to our wedding.

First, don't make her a bridesmaid if you don't know her. Something like that isn't really a way to get to know someone, which is often seen on here when people regret asking family members out of obligation.

Second, this is on your fiancé, not you. You mentioned that they don't talk much now, so that could possibly be why she doesn't feel the need to go. Just because she has the money or her parents would pay doesn't mean she has to be there. If your fiancé is upset about it (I don't know because you haven't really mentioned his thoughts or feelings on this at all) then it's up to him to reach out to her and try to figure out a solution. It's okay to feel bummed about it if she doesn't go, and I totally understand feeling bad for your fiancé and having compassion for him, but this isn't your thing to worry about.

"Am I in the wrong for thinking it is extremely selfish of her to snub her brothers wedding like this?" Yes, I do think you are in the wrong. You admit you don't even know this person, so how could you possible know that her decisions are selfish? There are so many reasons to decide not to attend a destination wedding and even though you think you have invalidated all possible reasons (cost, time, effort, travel stress, etc.), again, you can't possibly say any of that for sure, since you don't know her.

All of that said, even if she is the most selfish person in the world, there is no benefit to you to hold onto this grudge. You will only ruin your wedding experience for yourself. Plan your destination wedding, enjoy your trip, celebrate with your partner, and let each guest make their own decisions.

Also, definitely absolutely do not ask people you aren't close with to be bridesmaids. That rarely goes well.

I agree with this. Don't go into the marriage holding this grudge. Maybe it's rude, but let it go.

I agree with others that it's probably best if you try to accept her decision and move on. If FH is upset that she won't be attending, he should reach out to her and handle any communication. FWIW, I've been a family member for whom a destination wedding was incredibly inconvenient due to the time of year, difficulty getting time off during a busy season, difficult travel arrangements, etc. I tried to decline and was met with a huge guilt trip from the B and MOB. Ultimately, I felt like I HAD to go. For the reasons mentioned above, my family did not go with me. Because there are no direct flights and the time difference, I spent more than 36 hours traveling during a 3-day trip. By the time I got to the hotel the first night, I'd been up for 36 hours (worked all day, caught an overnight flight with a 6 hour layover, etc.). I was miserable. In total, I spent more than $2500 for a 3-day weekend, had to miss work, was separated from my own family, got home completely exhausted, etc. I guess I'm glad that I was able to be there for the bride and her mother, but they didn't seem to have a clue what they were asking of people. (Bride often commented on what a great deal the wedding was -- except she didn't seem aware that conservatively, her guests probably spent in excess of $75000 on travel, hotels, etc., so it didn't seem like a great trade-off to some of us.) That was nearly 4 years ago and, as you might be able to tell, I'm still annoyed that I let them bully me into going. It's a shame she can't be there, but please just accept her decision.

I agree with this completely! It's definitely not selfish of her because although it's her brother, she really has no obligation to be there and can choose to do what she wants with her life. I wouldn't ask her to be a bridesmaid.

I agree with this. Since you don't know her, and it sounds like neither does your fiance anymore, you cannot attribute any reason for her not going. You're the only one having hard feelings here-- an unnecessary stress. There are a lot of reasons why people decline destination weddings. If someone asked me to take a weeklong vacation, in a year's planning, I'd say, "nope, I have my own ambition to plan". Not everyone can plan their own weeklong vacation, much less take 2 in a year. It doesn't matter who pays for it.

Also, I'd ask persons closer to you to be bridesmaids and only in year 2022. Some friendships change, and maybe your relationship with the SIL might also. But, let go of obligatory bridesmaids, they bring misery.

There are thousands of cautionary tales on this very forum that illustrate all the reasons not to ask someone you barely know/don't like/feel obligated to be in your wedding party.

Normally I would say that people should always attend their siblings' weddings, but there are a few complicating factors here and some of them aren't divulged in the post.

Is she an adult (it sounds like she's married)? She has the money for a huge trip like this, but doesn't work? Does she have kids? Go to school?

If I were in the sister's shoes, I would be very hard pressed to go to this wedding. I would need to take a week off of work, spend two days in the airport, etc. to go somewhere I didn't choose to go.

Btw...$2500-$3000 per person is definitely not " extremely affordable, like, cheaper than traveling domestically". I don't think I've ever spent that much on a week's vacation, even our honeymoon.

While I understand that you're disappointed about FH's sister not seeming willing to come, I just have to say that I don't think $2500-$3000 per person is "extremely affordable." That's more than we spent on our entire honeymoon, and we went to Greece for 10 nights! A destination wedding of this extent is an extremely big ask. I would either let it go or have your FH reach out to her directly and express his feelings, since it's his sibling.