NTA I had a vegan friend apart of my group. If we were going some place without vegan options she would eat before going. Wouldn't get upser at anyone eating around her and all around a good person who was pleasant to be around. We had no issues with each other and I support their lifestyle.
The vegans like your sister I would proudly eat a steak in front of them, medium with the juice running down my face saying "mmmm tasty murder. Love animals as much as you, they taste delicious" and give the most ridiculous responses to any questions and accusations.
"Yes if people tasted this good i would eat them. No I wouldn't eat my dog but I'll eat one that's not a pet. Yup I'm animal hitler" you can't argue