Spoiled Little Sister, What do I do? Options

[eternalyfe]

I know this has probably come up a lot. But I am at an end with this.
My younger sister of 3 years is spoiled. My parents even know it but they accept it and shrug. She's boy-crazy, and will now only wear Abercrombie & Fitch clothing - much to the dismay of our savings.

She's a Freshman. I am a Senior. I think it's the high school atmosphere that's getting to her. She runs the house. She also has Type I diabetes (which means that she has to monitor her eating - and she sucks at this). Often, I will catch her sneaking food from the cabinets: hershey kisses, a spoonful of ice cream, anything that she really SHOULDN'T be eating. She had the nerve to come into my room and steal three or four packs of gum that I got for Christmas from my boyfriend. I know, it's only gum, but it got to me. My mom frequently buys small bags of candy to stick in her cookies or other things that she cooks, but my sister (I'll call her Ally) gets to them first. She will open the bag in private, take half out and leave the rest. My mom, mad at the circumstance and her ruined recipe, takes the rest of the candies out and actually BRINGS them into her room and SETS THEM ON HER DESK. I was so angry. No, I didn't want the candies. But I DID for once want for her to REALIZE that she's not the queen here.

Over the weekend I came down with a cold and have been eating cough drops like crazy for my sore throat. When I get sick, I like to read a lot. So today we had a big storm and school was canceled. I sat in the living room on the rocking chair and began to read. Not five minutes later, my sister came out and turned the TV on. Sighing, I shut my book (and she noticed this) and watched TV with her, waiting for the half hour show to be done so that she would finally give it up and give me some silence. 20 minutes later, she came back out, turned the TV on and popped in a 2 hour movie. I sighed again, raised the argument, but it was shrugged off. So I watched the movie with her. After the movie, she went back into her room. My mom came into the living room - told me she was going to go cross-country skiing. Dad was at work. So it was just the two of us: me and "Ally". I sat down again and was able to get a good 5 pages read when she came out AGAIN. She turned the TV on and then I couldn't be quiet about it. I told her about how the house doesn't revolve around her. We argued, more me than anything, she would turn the volume up so I couldn't even hear myself. So I sat there yelling over the volume, my glass cup of water in hand. Then she had enough of me, she got up, took a pillow and started actually beating me with it. (Yes, this is the same girl that pulled a knife on me when I was babysitting years ago.) She threw the pillow down and started scratching her nails at me. I have a bloody gnash on my right arm at the moment. I stood up from my chair, my cup still in hand and held my hands to my face to try and get through. At one point, the glass cup fell from my hands and shattered all over the tile floor. "Ally" screamed and ran outside with her cellphone. She called my mom up and mom came rushing home. I didn't know what the big deal was. I had the mess cleaned up (amid the deafening TV). My mom walked in the door, escorted me to my room and told me to stay in there until my dad got home. I AM A SENIOR! I was being treated like a child! I found out only a few hours ago that she claimed that I actually THREW the glass cup at her head.

I took the issue up with my mom (who, funny, was sitting with "Ally" in front of the TV). She got all sarcastic and shouted out "Okay everyone! So from now on! If she is reading a book and the TV is off, we ALLLLL have to leave the room." I rolled my eyes at this and continued sitting there. A few minutes later, unprovoked, my mom yelled "Oh, hey, is the TV too loud for you? We could always turn the volume down! Wouldn't want to hurt your ears..."

I'm fuming. I don't know what to do. I don't have the guts or the heart to "get even" with anyone. Yet all I feel that I can do is play the passive role.

What the heck do I do about this?