I'm sorry if I didn't catch this but is she young? Like 20? Just curious

If you feel she is over stepping the line... then she needs to respect your boundaries and there was norhing wrong with you telling her not to add your close friends, even if she didn't react well. Thats the right thing to let her know, maybe she thinks you just love her constant company, but in reality she's being intrusive. Some people like being in each other's business, but most of us don't.

This seems like my life. My car got scraped and inside was trashed, she contacts the guys I dated, and talks to them without me knowing! There was little respect, she badmouthed me to my friends and ex's. I once thought that she just wanted friends and to feel like she belongs. Just because she's your sister is no excuse for allowing certain kinds of behavior. SHe's okay to share my friends, and come along, but what she did just ruined it.

That's the thing with living together too. My husband's sister used to barge in his room when we're watching a movie, and take eat food (in front of us) that I bought, kick us out while drunk cause she wanted to watch baseball with her BF, and invite all her friends when my then-BF wanted to make my birthday dinner. Inlaws are worse, but that's another story. I want to keep the realtionship but they just ruin it!