I tried a few things, with varying success:
I held the line on a cake. MIL wanted one. I didn't care that much. But I could tell as soon as she got the cake, she was going to move on to something else. So I just kept going back and forth with her on the cake. I thought that would contain the damage. She was obsessed!!! She told everyone about the cake. She brought it up every time she talked to my how-husband. Cake cake cake cake cake.
by holding the line on the cake, I was able to keep all her crazy focused in one place. Then I was going to give up at the last minute and let her have a cake. But I forgot. BIG MISTAKE!!!
I also tried to follow my husbands suggestions for including her. I thought it would get me points and maybe make things easier. He's dealt with her longer, so maybe he knows how to handle her? Another BIG MISTAKE. She loves him. She does not love me. He believes her when she lies. I do not. These two factors matter more than I realized.
I had bridesmaids taking turns on MIL duty at the wedding. This was helpful, but in practice it ended up with situations like "MIL won't let them put out tarts and we are out of food." So I say to put out tarts, and she goes behind my back again. I ended up sending my toughest sister after the staff with the order for staffers to "get some goddam tarts on a fucking plate right the fuck now..." (Real classy, I know). She got it done and told me later... "I didn't yell... Exactly..." I suspect I don't want to know how she was able to get past my MIL. Three people before her had failed. I think MIL was trying to make everyone go home/ruin the wedding in retaliation for the cake. Her only explanation was "I thought people should wait for dessert." A similar thing happened with the band.
If I could do it over again, I would recognize that my first instinct was right. That I couldn't expect my husband to spend our wedding fighting with his mother. And just instructed staff to only listen to me. I thought it wiould be easier to be less hands on, but it wasn't.