My (33f) sister (29f) is a vegan and her diet sucks the joy out of family meals.

I just want to start with a disclaimer that I'm not against veganism, just the way my sister behaves as a vegan.
My sister has been a vegan for a little over a year now and it ruins every family meal we have together. She lives a couple of states away so this is generally only an issue around major holidays. She's coming to my mom's for thanksgiving and everyone is already dreading the meal because of her behavior surrounding non-vegan food.
My sister isn't someone who can keep her dietary preferences to herself. She's also the lone vegan or even vegetarian in our family, everyone else is an omnivore. When she transitioned to veganism from vegetarianism nobody gave her any trouble, but we didn't go out of our way to be accommodating either.
She transitioned fully to veganism like a year ago and got a lot more involved in the ethical aspect of her diet. She's definitely a 'preachy vegan' and seems determined to shame everyone into eating the way she thinks is right. She uses meal times as an opportunity to 'educate' us about the horrors of the meat industry and how we're polluting our bodies. She will try to have philosophical debates about the morality of killing animals to eat them.
All I have to say on this subject is that while I recognize the meat industry could absolutely be more humane and if I could choose to eat lab-grown meat instead of having to rely on slaughterhouses etc I would, but I'm not going to stop eating meat and I'm pretty sure nobody else in my family is going to either. The problem is that she won't drop the subject. Every meal is the same.
The other issue is that she wants to feel included and supported and expects that we'll provide food for her. In my opinion her preferences are the minority in our family, and if she wants to have a meal with a bunch of other people who don't share her diet she shouldn't expect people to go out of their way to cater to her, but that's exactly what she does. My mom tried initially to make some vegan meals or side dishes for her but my sister always found something wrong with them. They're not organic, sugar is made with bones, the quinoa isn't ethically sourced, etc etc etc. It never ends.
Now she's talking about transitioning to raw veganism and I'm afraid that her behavior is going to escalate even more, to the point where I won't want to be around her. I'm not going to tell her what to put in her body, I just want her to shut the **** up about it and stop telling me what a horrible person I am for my own choices. I honestly feel this is the same sort of scenario as a person who is staunchly against abortion using every possible chance to bring it up and rant at people about it. That's not socially acceptable, so this shouldn't be either.
I don't know how to say this in a loving way that won't make her feel like her family is against her or her beliefs. I know it must be lonely to feel so passionately about something and not have your family share your values, but that's the reality of the situation. If she would just drop it and make her own food to eat at family meals, everything would be fine. How do I set a firm boundary on something like this and enforce it without alienating her??
tl;dr: my sister is a very preachy vegan who doesn't seem to understand that freaking out constantly over my omnivorous family's diet isn't going to do anything to change our preferences. How do I get her to shut up about this without totally ruining our relationship or family celebrations?


Source.

This really hard abit...but u continue to pretend as if all is well.

Pour gravy on her food and tell her y'all are tired of her bull****