what do I do? copying me

I just don't know the best way to handle this: so I have a SIL who I dislike for many reasons. But two of the biggest reasons is she is a liar and a narcissist. So maybe that makes the problems I'm about to explain magnified because I dislike her. But she basically tries to copy everything I do. But not just copy, it's like she has to "be better" or out do me. And it's to the point that I barely share any of my life on social media which I find horribly frustrating because I feel like I shouldn't have to "hide" my goals, projects, wants, and general life. especially whwn i have family/friends who are put of state and i want them to keep up with me. I also basically have to hide every aspect of our life from our family because if she catches wind of anything, suddenly she is doing it too. example: they bought a house. great fine and dandy. we were out of state for a while and we are moving back and we were debating on buying or building. we decided to build and told mine/his parents. suddenly she wants to sell her house and build. I talk about wanting to upgrade my lens for my camera and she bought the one I wanted. And how hers is better than the one I wanted because she spent 900 instead of the 600 mine cost. I never even said a word to her about it. someone asked about it at a family function that she happened to be at and she text me a few days later saying she bought it. I could go on ALL day. I can't unfriend/block her on social media. And again I don't think it's fair that we basically can't tell any family what we are doing/what we want to do without it somehow getting back to her. I'm just so frustrated. edit to add: I married one brother and she married the other. (if thats still confusing: my husbands family is just him and his brother. bo other siblings. i married my husband. and she married my husbands brother)in her own family she has a brother and a younger sister.