I Hate My Cousin. She think she's grown! Help!!!! She gets on my nerves!?

Im 15 yrs. old. I Love to sing, Dance(kind of), Write my own songs too. I'm going to be a sophomore next year! My Cousin just finished high school! When, we were living together in the same home. With my grandma, She would always pick on me and tease me about what I do. She tells me, That my singing don't get any better as I go on trying and trying. Because, I want to meet mariah carey one day! Because she's my favorite singer! I want to record with her! Anyways, My Cousin always picks on me about my friends and my "butt"! She tells, me that I have no friends. It's only associates! She says, That she have all the friends in the world. (SHE'S A SLUT!). She have a boyfriend. Tells me that I need to get one. When, I say. You know my mom won't let me you idiot! Then, She tells me that I do childish things. Like argue with her when, She starts it. She is such, a bully to me! We use to go to the same high school. But now she's in college. (thank goodness). But she stills brothers me on facebook. Says that I had naked pics up of my self. Which, We all know face book do not allow! She's so stupid. Her boyfriend is only using her for sex. When he ask her to give him some. She do! Everytime. When, I say, Your hurting god. She's Like. I Don't care. I was like. When, Youre gonna not give in to him? She was like today! Then , the next minute. I know. I hear bangging and moaning in my grandmothers room!!!! I was like you slut! She's popular too. Really popular. I am an ugly duckling! I am one. Believe me! I hate it! Im the nerd out of the whole family!!!! Even the little kids in my family pick on me! It's irrateting! I can't help it. I Won't tell my mom. My cousin will only make it worse for me! My Cousin's boy friend calls me childish. Because I kicked the door by accident when they were having sex. Which, I really didn't know. But i suppose that they did. But it was an accident. The second, Time wasn't cause, I just took the door knob off to get her back. When, I give her money. She never ever pays me!!! Her or her boyfriend! They just use me and my money. I over heard them talking about me. Calling me a childish brat. Then, She said, That she hates my guts! My Cousin's boyfriend is like 21. She's 18. He called me a spoiled brat. Because I work for what, I get. She don't! She always used to make me do her chores. When, we were younger and she still did make me do them! She have a 2yr. old he's so cute! I Love him to death! She abuses him! For no reason. Verbal abuse. She's a slut. Because she slept with our grandfather , when he was drunk to get some money! Then, she gonna say. Oh, He raped me. But, my grandma . Didn't believe any of that crap. Because., I Had the whole thing on video! My grandfather knows better then to do that. Only when he's super duper drunk and don't have a clue. That's when she did it with him! Or tried. My grandfather told my grandma first. My cousin was like no i didn't he raped me. Good thing , I had the video from the very first start of it! Slut! My cousin hates me for that still. She's super bossy and mean to me still. She talks crap about my mom and says she hope my mom dies and stuff. My mom is the only person I got her besides my grandma and two of my best friends! She talk crap about my grandma too! She uses her! My grandma don't even know it! It's getting on my nerves! My cousin only calls me or my mom when she needs something! Which, We don't talk to her anymore or really call her. Because she thinks she can get away with stuff! And not get caught. I told my mom everything! My mom hates her guts. But still, Love and forgive her. But, She won't do anything for her! My Cousin harasse me on facebook. That's the thing. I'm afraid if we have a family reuinon in like 5yrs. I may look better then her. Because, Im the ugly duckling of the whole family. They always say, Im a be a singer one day. Because, I don't give up! My cousin do! That she will probably try to bring me down. That's what I worry about. I need help!!! With her!