OP was NTA! (11/22)

The tantrum thrown by OP’s SIL was absolutely worthless and had no meaning to it. She knew very well that OP does not eat non-vegetarian food and hasn’t been eating it for over 10 years. Had it been just a few weeks, this “mistake” could’ve been acceptable but we are talking years here. A simple solution to this could’ve been a separate meal cooked for OP. She had already decided she was going to cook all that food that was going to take her 3 hours to cook. She could’ve cooked a non-vegetarian meal simultaneously which would’ve taken 30 to 40 minutes max, and OP would’ve been a happy woman. 

SIL being all dramatic about the situation shows she is the true AH here by staying at OP’s house and not respecting her dietary preference.