He won’t listen to me and I’m too wound up to talk calmly about anything :((
As you said, you can discharge a fair bit of this in your next counselling session.
It might take a few sessions! - but how about using some of these as role-play for how you will handle the situation next summer?
Roleplay is helpful as you get to experience that jolt of feelings - the same feelings that are so scary that they often shut us down - hence your seething in silence. Remember your worry that if you DID say something, suppose MiL countered, & how would you respond ...? Get those feelings out there in the safety of your counsellor's room. See what it feels like to go in tactfully, to go in 'surprised', to go in angry or hard. What it feels like when your counsellor responds as if she were your MiL.
It's far less scary when you've already practiced dealing with that jolt of emotion.
That feeling of confrontation/fear/overwhelm/being able to carry on speaking.
There's no point beating yourself up for not tackling MiL previously, & you're right, it would be ridiculous to move out to avoid her next summer. So practice scenarios - see what's 'easiest' for you, tackling in the moment, or a pep talk before she even sets foot in your kitchen, eg
"MiL, last time you were here I was puzzled that you deliberately excluded the kids & me from your cooking - we don't do that in my house, we look after everybody. So let's have a chat about meal plans, who cooks what, & how to include everybody." might be a soft way to introduce it.
Or you could 'give her enough rope' - let her barge into your kitchen & act like you don't exist, & challenge her - "WTF are you doing, just cooking for the men & yourself? This is my home, & my kitchen, & I will not be treated like a second class citizen in it. Either cook for everyone, discussing it with me first, or get out of MY kitchen."
More immediately though - you also need to roleplay talking to your husband, who was a wet blanket while his mother was treating you so bizarrely & is now protecting himself by refusing to discuss it with you. As you can't yet address the subject without losing your cool, (hardly surprising) you need to be in charge of yourself & your reactions so that he has zero excuse to shut you down or call you unreasonable. So even if it takes a few sessions before you are ready - something like "DH I know you don't like talking about this but if MiL's summer visit is going to have any chance of being a success, these are the ground rules ... btw I will NOT be shut down by you on this subject, & I will NOT be treated as if I don't exist by your mother, so it's in your best interests to work with me on this"
You need to make him understand that continuing to stonewall his wife will have worse consequences for him than standing up to his mother.
I wouldn't ask him to tackle her on your behalf either - he'll either fail to do it, or he'll muff it, or he'll make you out to be the crazy, demanding one who he has to pacify. Deal with her yourself. Remember - it is YOUR KITCHEN, & what you say goes. DH doesn't count as a kitchen owner in this scenario - he hung you out to dry to appease his rude mother. He's still doing it now - his slight discomfort about discussing it with you seems to be far more important to him than your wounded feelings.