To paraphrase Grey’s Anatomy, there is a land called Passiveaggressiva, and my mother is their queen...
On the assumption MIL has form for sulking, tantrums, emotional blackmail to get her own way and there is a history here, I shall translate the meal and portion size as follows:
I didn’t get what I want and expected is my right that my son should come to me for Sunday roast on Easter Sunday. As his mother and the most important person in the family I did not need to arrange this in advance as everyone should just know this is what is to happen, and even if they did not, it is what I want therefore it is what I get.
I am outraged to be told that, not only does my son have the temerity to have other plans, but it is with his in laws - which is the biggest insult to me that he does not want to see me instead and must be under the thumb of his wife (who I’ve never liked) to go there instead of here.
I have cooked a roast, and me and my husband will eat ours. On the Monday I’m not making more of an effort, but will warm up the leftovers to subtly express my displeasure. I shall await comments that the portions are tiny / doesn’t taste right as I shall have the glorious opportunity to say “well, if you’d been here yesterday [like you should have been] it would have been lovely”, and also I get to make them feel miserable and hungry as a bonus.
Am I nearly right? If not, I’m projecting wildly on the basis of my own experiences, but unless you’ve experienced this level of passive aggressive nonsense and knowing precisely what message is being sent to you it’s hard o explain to others without you looking like the bonkers one..
Can I ask what your DH thought - if he tried to minimise or say that’s what she’s like then I’m guessing he’s had years of similar behaviour to endure.