We’re doing a key west Destination wedding, and my Mother in law is not happy

Hey everyone! Just wanted to see how people handle their families that are not happy they’re doing a DW. Before we planned anything, we had asked my fiancé’s mother if she would be alright with it as she has a fear of flying and she said “yes sounds like fun!” money is NO object so now that it’s planned she is acting super down about it. None of her six sisters are invited and she’s bummed and I understand that. My mother passed a few years ago so I truly value our relationship but man her behaving this way makes me miss my mother so much! My fiancé and I never wanted a big traditional wedding we’re both fairly introverted and he gets panicky At big events. so how do I handle her and not spout off at the mouth with “it’s our wedding why can’t you just be happy for us and then go talk behind our backs like a NORMAL person!!?? 😂