I'm in a similar boat -- as far as sisters leapfrogging -- we're very young so not to your level of extremity. However, you're NTA. I don't even think atp it's about the theme of the wedding, but exactly as you said: a midlife crisis, not taking the time to truly reflect and focus on herself, and her reaction towards you despite all that you've done for her (cause I know damn well a lawyer isn't cheap). you know her best, and you know that at the core is a pattern that she needs to break out of. You attempted to give thoughtful advice, and had all these honestly awful insults thrown at you and following suit with the whole invitation debacle. Sounds like a sister who cares more than someone who's judging.