Problems with my sister..what should I do?

My sister has treated me horribly my whole life. She both physically and mentally abused me starting at the time I was 5. My mother knew but my father didn't and my mother didn't do anything about it since we were only living with her for a couple of years. She is 21 and I am almost 20. We are both engaged now and I went to Hawaii when my fiance had work there. She and her fiance told people around my town that I was a prostitute/had a sugar daddy. Her fiance, who has only spoken to me about 10 minutes total in the 5 months they have known each other calls me names behind my back and talks badly about me to other people. Just today I found something that my sister had written 3 years ago or less (I know this because she has her daughters name on it who was born 3 years ago). It was a note card that had my name on the front. The back had the definition of "me" which was monster;spoiled brat. Antonyms were: her name, her daughters name, princess. That doesn't sound bad but the synonyms really make me feel so horrible. Synonyms are: godzilla, satan, crack dealer (I have never done drugs in my life - she used to smoke pot and her fiance used to do cocaine) and the worst - Osama Bin Laden. I want to expose her to everyone by posting pictures of this notecard on facebook. I have dealt with this my whole life and to be called someone so horrible is absolutely repulsive. Can someone please give me advice? My parents can't do anything because she threatens to not let them see their granddaughter if they say anything against her. I can't deal with the way she treats me/the things she says about me and advice on what to do about the situation with her would be very helpful. Thanks so much.