My sister is very rude and mean? Please help?

My twin sister has always been more on the rude side especially these past few months. My best friend knows how she is and sometimes I can tell it hurts her when she makes comments. She doesn't know how to keep in her anger. If things don't go her way she is set off. She will just start yelling and then try to talk to me and then later will yell at me again. It's affecting my whole family. In school she gets annoyed by this one girl and one time she yelled at her in her face telling her she was so annoying when she wasn't even involved in the conversation going on. She walked out and I was in the classroom as everyone was saying that she gets mad all the time. When she flips out on people people give me looks as if hey are in shock and I feel so embarrassed. Sometimes I wonder if she has anger issues and it just makes me so upset. If I try to talk to her about things like this she gets so angry and I just don't know what to do anymore. A couple of minutes ago my mom told her to put the dishes away and she didn't listen until my mom raised her voice and told her to put it away. It then escalated very quickly and she told my mom to shut up. I feel like my mom is sort of giving up and she stopped yelling at her for talking to her in that way. It makes me very upset. There's much more she has done and over the years over the dumbest things and I just don't know what to do anymore. I wish it wasn't this way everyday. What can I do?