Y'all gotta know what I'm talking about

I'm arguing with my mil about my food choices, Ik stupid. I have been a vegetarian for years and last year tried shrimp and got allergic. I read somewhere that foods your body isn't familiar with can cause sickness/allergies. They swear I need to try sushi and shrimp but let alone to me being allergic to shellfish it's not worth the risk of cross contamination. Can someone help me find an article or give me the facts to present to her. I tried google but can't find what I need! Thanks!