family member from hell?!

a little background: my sister knows everything. she always has and she always will. you could invent a subject and she would find a way to become a google certified expert on it. no one knows more than her. not even doctors in some cases. she also blows up nuclear style if you stand up to her and yet has no idea why the entire family tiptoes around her. shes turning 40 soon, has been married about 10 months longer than I. her and her husband are constantly on the brink of divorce. she hates her step daughter with an unreal fierceness. she has never wanted children.

until she found out we were actively trying and were even doing fertility treatments. so she suddenly wanted a kid. I turn up pregnant before her which I'm sure was a problem for her. she decides shes going to buy me a book about her lifestyle. my sister is a fad dieter. whatever the newest craze is shes the most dedicated. she went from raw vegan to a meat and cheese scarfing keto eater in a week. so this book is about her lifestyle and diet and pregnancy. it literally shames you if you aren't eating and living like her. ot literally says your baby will be less intelligent and less successful in life if you dont ascribe to that lifestyle of extreme carb deprivation. meanwhile I can pretty much only eat dark wheat bread with peanut butter without getting sick and she knows it.

my family doesnt want me to stand up to her ever because she turns it into an all out war and brings them all into it and if they dont agree with her side she flips on them too. there have been months and years that have gone by that nobody talks to her because shes so volatile. meanwhile I cant understand why she would choose to try to shame and stress me during this time of my life.

anyways I'm sorry. I dont really have anyone else to talk to about this.