I believe there was a huge hooha about it at the time and the husband was arsey because he was getting it in the neck from his mother over "her party".
The thing was, friends sister was finally, really, really pissed off and their marriage was very unstable for a while afterwards.
Lots of pent up bad feeling on the wife's side and I think her husband had just been preoccupied with keeping the peace and didn't know his wife as well as he thought.
When he realised the marriage might end he turned it around but as I said she was very upset for a good while.
They stayed married but she never allowed her MIL to get away with any imposition again.
However, the MIL did back off when her son told her the marriage was in trouble.
Some women do think they can dictate what their children do beyond adulthood. It makes for unhappy marriages though.
I think unfortunately it's a mistake to be too passive and accommodating around domineering people.
The idea that a MIL would arrange a party with out consulting the mother of the child and exclude the mother's side of the family is just madness. Putting up with that type of bullshit is never going to end well.
I couldn't look at a man who would think that was reasonable.