My twin sister is snooping through my stuff and is threatening me?

My sister and I are both 15 but we're totally different. She's very quiet and shy and nerdy. So since last year shes been really snoopy. She goes through my phone and looks at my pictures and texts, she stalks me on facebook, and she looks through my wallet, bags, and my room. Sometimes when I get home late, she gets close to me and smells me (for smoke or alcohol, idk). Its starting to get kinda scary and creepy now. She found my cigarettes last year and she saw some pictures of me partying and pics my bf sent me and she was like IM GOING TO TELL. so I had to pay her to stop. She always barges into my room when my bf is over (luckily we weren't doing anything yet when she comes in). So she found a few used condoms and my hookup list and shes threatening to show my parents the condoms (GROSS) and put my hookup list up on facebook! I think shes also angry because there was this huge party that everyone was going to, even some of the nerds(like her). But you needed an invite to get in. I only had two more invites left, and I had to give them to my bffs. She was super pissed, even though she doesnt drink and I knew she wouldn't like the party anyway. Why is she doing this and how do I stop her without our parents involved?