Last year I posted the below thread -
www.mumsnet.com/talk/am_i_being_unreasonable/4537340-wwyd-family-member-spoiled-our-night-out
It's long, but the basic facts are, I went on a night out with a cousin who totally ruined the night and for reasons I still do not know the answer to, threw a drink in my face.
I didn't take all the advice I was given on here, I told my parents and siblings what happened but asked them not to discuss wider than that. The cousin has never made contact with me nor me with her. Weirdly months after the event she also left the family Whatsapp group and deleted me from Facebook. It has never been mentioned by any other family members and although it did take me a while, I'm over it and content with the no contact.
The problem I have now is that the sister of this cousin is getting married this year. She is absolutely lovely and we are good friends, I wouldn't dream of missing her wedding or doing anything to spoil it. Should I mention what happened last year in the lead up to the wedding to avoid potentially awkward seating arrangements, or will that cause the bride unnecessary stress? I don't think I'd even need to go into all the details, just that something happened last year and we haven't spoken since. I have already decided that I won't be drinking and will leave after the first dance as I don't want to be around the drink throwing cousin in any situation really, let alone one where she is drunk.
YABU - the bride doesn't need to know, leave her in wedding planning bliss
YANBU - mention it so the bride is aware and can plan accordingly (I'm thinking of the seating plan more than anything)