I understand!!! I think corn would be worse though because as you said, it's in nearly everything i n one form or another. DD2, DS and I have an intolerance to onions and all alliums, and peanut butter. At least we can recognize if there's garlic or onions in something. DS has many more allergies and intolerances besides. DH gets very sick when he eats hazelnuts or commercially dried coconut.
I never want to go to any social function because there is nothing I can eat. People say just bring something you can eat. OK, I'd rather stay home and have a full meal than to go somewhere and only have one or two things to eat. We are vegan as well but most of our friends are too so that usually isn't a problem. There are a couple of ladies at church that are so kind to make us a small amount of many things they bring to potlucks and social functions without garlic and onions. I appreciate that so much!
It's weird that you MIL does that! I know some of DH's relatives doubted my lactose intolerance and would "test" me with dairy in things. They saw me sick enough to believe me. It didn't take much either, even whey in a flour tortilla would do it.
What are your symptoms? Mine are stomach/belly pain, loose stools, insomnia, and then for about 3 days it feels like my entire digestive tract from the stomach down is irritated. It's sore and burns.
I wish I had advice for you but I just wanted you to know that I understand!