If you'd asked me what to do before you got frustrated with your sister and expressed it, I would have encouraged you to be a bit gentler with her. The commentary about insanity and moving on was unnecessary. She's obviously very hurt (making irrational demands, yes; but in pain, too) and didn't need to be told anything that would make her feel worse about herself.
Guest Jimmy Fallon asked Kelce whether he and Swift had started the wedding planning process, and specifically wanted to know about the music. "Are you gonna do DJ or band? Are you thinking about all this stuff?" he asked, with Kelce revealing, "Yeah, I think we're live music kind of people, you know?" That might also include karaoke, after Fallon praised Kelce's surprise karaoke performance with his brother, Jason, in July at the American Century Championship.
You can be proactive about this and you can make a plan for de-escalation if your prophylactic measures fail. Mother and daughter being close is a wonderful thing. Being 'prone to fighting' is not.
Planning a wedding is exciting, particularly creating a registry where you can select everything from kitchen gadgets to home decor just like online shopping.