My 7-year old sister is driving me nuts!?

I am 12 and my little sister is 7. She is sweet and caring, but sometimes she acts really bratty. Last month I bought a new dress that I was going to wear for my best friend's party, and my little sis completely destroyed it! I was in the shower and when I came out she was in the living room eating a yogurt.. With MY dress on!! She stained my whole dress and I had to wear some old clothes for my friend's party.. We were supposed to be matching dresses. She was wearing a blue one and I was wearing a red one. Both with the same design:(. Then the other day she told me a friend had come to visit me and so I got out. When I realized she lied, she had locked all the doors and windows. It was hot outside. It was about 90* F. An hour later my sister opened a window. When I got inside she had my phone in her hands. She said that If I told my parents she had locked the house, she would restart my entire phone, so I didn't told my parents anything. I mean, I have my cousin's and friends' numbers that live far away. Lastnight she woke me up like at1 am to help her with her honework. I was furious. I helped her and then when I got to bed she wouldn't turn down the volume of the TV. I am really tired. I tried telling my parents but my sis acts like a goody two shoes and they don't believe me. Should I yell at her? Should I somehow stop her from doing that? What?