I (f28) have been a vegetarian for over 10 years, and all my family knows and respects that. Even my sister-in-law (f25). A couple of times a year my sister-in-law and brother (m24) visit us in New York from Florida. Usually my sister-in-law will cook something for one of the nights that they stay for dinner.
This time she ended up cooking a roast chicken dinner, with beef rice, and a shepherds pie, which does have ground lamb. I told my sister-in-law that I couldn’t eat that because I’m a vegetarian, in case she had forgotten. She told me that she spent over 3 hours cooking and that I was going to deal with it and eat it, or not eat for that night.
Note from OP: 'She did not cook it in my kitchen thankfully.'
I told her to calm down and that I was just going to make myself a salad. This made her break down in tears saying that I was disrespectful to her and the hours she spent cooking. While this was happening I just made a salad and ate it in the living room.