What should I do about my sister?

She is 17 and I'm 15. Normally she acts wonderful and never gets into trouble. But Herfriend was loud and obnoxious and rude. My mom yelled at her friend because she was slamming doors and throwing things. Then, she said she didn't have any money to pay my parents back for 25 dollar tickets and a 10 dollar dinner. Worse, at the cabin we had rented, she took a rock and scraped the finish off of the outside table! Then my sister scraped the paint off the closet with a hanger. She didn't mean to but if the owners find it they can charge us a lot of money. I told my mom how the paint got chipped because my sister kept lying and saying she didn't know how it happened. Then my sister wrote all over her body with sharpie. So when we got home, my mom told her that she didn't want her hanging out with this girl anymore and that she knew the closet wasn't like that when we got there. She said my sister and her friend would have to pay for the damage if they called and that she thought her friend was rude and disrespectful. She also said she looked really cheap with the sharpie. Then I talked to my sister and said that maybe she should look at it from her point of view. My sister is really mad at my mom for not liking Sara and telling her about the sharpie and what not. Then she told me to stop trying to be the piecemaker and just shut up. I said that nothing will get better if she doesn't stop and look at the situation. Finally I said I was going to bed and that she should think about it. Then she kept saying maybe you should shut up and go to bed. I get that I was bothering her but I really don't want things to be bad in my family. So I just kept saying that maybe she was wrong and she should take advice and just stop because she wasn't seeing the Other view. she told my that I was fat and ugly (I weight 98 lbs) and that she hates me and I should kill myself. I know she was just mad but it made me cry; I don't knOw what to do. I'm very upset about it. I just wanted to help.