Sorry, I was extremely angry when I posted but I guess I should give some back story.
My mom raised me to be respectful and tolerant of others - faith, creed, opinion, pet. Everything.
My SiL is not of that view. Everything is a competition. She once started an argument in which she claimed "pure" Lutheranism was a "better" faith than Zoroasttianism. We are part Parsee on my Mom's side so this was deeply offensive to us.
Another time she told me that crochet was anaesthetic and dumb when she knows my Aunt is an international crochet player. (Or croquet?!??)
She has raised DP's neice in the same way.
So I know this isn't a competition. But the other side don't.
To make matters worse my DP is siding with his sister and has said DD is being - literally - a 'silly newt fancier'.
I'm really at a loss and now my relationship is at risk too.
Looking for genuine advice from others in the same position.