MIL constantly commenting on my son's 'poor' diet

My son is 18. He has autism, ADHD, and sensory processing disorder. So does his dad. He doesn't really like anything. It's hard to go out to eat with him because he just doesn't like anything. He eats like 10 things. A big one is Mac and cheese. He works at Walmart and has worked there since he was 16 and is constantly buying that microwavable Panera bread Mac and cheese. I swear he eats it like 5-6 days a week. My MIL is always commenting on my son's eating habits saying he's too skinny for his age and that I don't feed him right. He's on the lower side of weight for his height but still average. My MIL keeps saying I don't feed him enough and how she hopes he gets a wife who will actually feed him because I'm doing such a terrible job. I feed him. He just doesn't eat everything I make. He learned to make some simple things he likes that aren't Mac and cheese but she said every time she sees him he's eating Mac and cheese and I'm teaching him to go for a woman who can't cook. I need to be the example of the type of wife he needs. Like first off, he has never shown any interest in girls. Second of all he can have the female Gordon Ramsey for a wife. He still won't eat probably 90% of the cooking. She says maybe I'm just bad at my "womenly" duties and hopefully he finds a wife who will feed him 🙄