Dear LW, definitely go after your grown daughter about your brother's family's feelings about how happy she was at her wedding and how they were insufficiently recognized at the event! I am sure she couldn't possibly have had anything else going on or have any reason at all for not wanting to talk to people who would carefully keep score of what she was doing and who she was speaking to at the event and nurse up offense to bring up with the rest of the family and not directly with her later. She will certainly admit she was wrong and want to spend every holiday and weekends too with her family going forward if you chastise her on behalf of your siblings, as they have asked you to do! This is 100% your problem to solve, get in there and chew her out properly, how dare she enjoy happy memories of a perfect beautiful wedding centered on her and her husband!