Ladies and Alcohol

I decided to drop something on this as a result of a challenge I am faced with tight now and I would love to get advice on how I can be of help to this lady. We have been friends since our high school days and we actually met when she came over to my school back then for summer classes, she attended a different high school. We got closer as good friends when we were about securing our admission into the same university. It was great having both us in the same university, liked her and took her as my sister. I didn’t know too much about her but I always tried my best to do that whenever we were together. I felt so bad when I got to discover that she takes alcohol. According to her, she has been doing this since she was in high school, I wasn’t pleased with this and I tried what I could to stop her but it generated into something else likened to be the beginning of we disliking each other. I tried advising her and I was also scared after she had told me about several attempts of rape on her whenever she was drunk. Right now, we are not as close as we used to and this started when I brought up this issue. How best can I go about addressing this? I need to stop her before it’s too late.