In laws 😒😒 share your stories

I can't stand my sister in law she's so annoying, has the worst attitude. She's 21 & acts like a 15yr old. As much as I try to be the bigger person and ignore her she irrates the hell out of me. How do you girls deal with sis in laws or in laws. I want to be the bigger person always but sometimes I want to tell her off. How do I ignore her without cussing her out? Share your stories!!