Best friend is choosing her fiancés family’s wedding over mine

Well, what do you expect? You already kicked her out of your wedding party. It's usually a friendship-damaging, if not -ending, move. Why should she choose your wedding over her soon-to-be family member's wedding after that? You just described her as cocky, flaky, and self-absorbed. Doesn't sound like you think much of her anyway.

What was it, exactly, that caused her to get kicked out? Absolutely no need to go into it if you don't want to, just curious as there's potentially more nuance to the situation than we could possibly be aware of. Most likely you were justified in doing it, but then it's also understandable that she would feel, based on that action, that it would be better for her to attend this other wedding.

Not passing any judgment on anything, totally understand your frustration. But If I had to go as far as to kick someone out of my wedding party, I would absolutely not be surprised if they decided not to attend. I agree with Vicky that, based on the limited information we have i.e. literally just your wording on this post, she doesn't sound like one of your favorite people and that this is a friendship you may both want to re-evaluate. For right now, my only advice is to try to forget about it as best you can. You can't control what she chooses to do, so focus on what you can control: your wedding planning! Good luck.

Exactly this. Doesn't seem like she is your best friend, IMO, if you kicked her out of your bridal party and describe her that way. Without knowing the full story, this is definitely a bridezilla moment on your part.

If I were she, I would choose to go with my fiance as well.

I mean if I got kicked out of my best friend's bridal party, I wouldn't go even if I didn't have a wedding that week. Seems like you two aren't in a good place and it's probably better she isn't there so you aren't in a bad mood on your wedding day.

I mean, what did you expect? You kicked her out of your bridal party… I wouldn't attend somebody's wedding either if I were kicked out for that very reason, let alone the other wedding.

I wouldn't come to a wedding I was kicked out of either.

You definitely have the right to feel hurt about this, but if she was removed from the bridal party then it's not totally unexpected for her to choose to attend a different wedding instead. Thankfully she wasn't still part of your bridal party when she told you she could no longer make it!

I'd venture to say your "best friend" isn't the only one who's self absorbed. And add me to the list of those who would stay home even if I had nothing else to do once you kicked me out of your bridal party.