Boyfriends sister is crazy, advice?

My boyfriend and I have been dating for 9 months. We are in a serious loving relationship. We've known each other for 2 years. Since the beginning we were close and he'd talk to me about his family. He use to tell me how he hates his sister and she's evil. I always told him she couldn't be that bad. A month or two into the relationship I met her at his graduation from college. She was not extremely friendly and kind of cold. I was nice regardless. She was by no means the witch my boyfriend had made her out to be, or so I thought. Just some background on her. We attend the same college and are both freshman. I'm older by about 10 months or so. Her mom told me she doesn't do well in school and maybe is jealous of that. She flipped out a month ago because I drank "her" iced tea. Her mom offered it to me and sometimes buys food for me too. His sister ranted and screamed like a baby having a tantrum. I've never confronted her about anything and I am very polite regardless and try to avoid her when possible. I rarely see her when I'm over his house. I've seen her once since the iced tea incident. She ignored me and I said hi to her and the rest of his family. His mom thinks their older brother put her up to some of it because apparently he likes to meddle? I don't know. Anyways today I wasn't over there but she had a tantrum over me. My boyfriend went to go talk to his mom. She made him a sandwich and he was like thanks mom that was super nice of you. His sister overheard and just went nuts. She started yelling at him to get a life then started ranting about me. She said that I talk sh*t about their family and about her and her boyfriend. Then she told him I'm fat and ugly and have a horse face. She also said that I am tearing their family apart. First of all, I have never talked sh*t about anyone in their family. I love his parents as if they were my own and they are really good to me. I have been nothing but nice to her. The fat and ugly part really hurt me. I am all upset now because I have poor self esteem as is. Anyone out there have advice on how to handle this situation? Talking to her is out of the question. My boyfriend said she's way to ignorant. I don't know what to do. I feel so uncomfortable. I'm afraid she's trying to sabotage my relationship with my boyfriend. I don't understand it. He's always been nice to her. She's just a witch to him and their family, She's nice to his brother and sister in law who just had a baby. At first she was a witch to the sister in law and was really jealous cause of the baby. A few years ago the next door neighbor broke in and attacked my bfs mom sister and dad. He was upstairs ran downstairs and kicked the living crap out of the guy and saved his family. Everyone is so grateful except for his sister. It didn't change the way she treats him. She is still rude etc.

Sorry it's so long. Any advice would be great. Thanks guys :)
Boyfriends sister is crazy, advice?
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