How can I talk to my sister about her drug problem without her getting defensive and/or leaving?

if i have to talk about that stuff i will try to explain the same matter using someone else story so no one would be ale to know that who is the real victim

Start slow. Also start from a place of compassion and concern. Let her know how much you love her and that your with her. A lot of drugs addicts feel like your attacking them when you're really attacking their addiction. In the end though, any solution will be up to her.

Drug addiction can be a huge problem, and people who are addicted to it often will be defensive when they are told that what they are addicted to is bad or they need to stop. Maybe instead of telling her that what she is doing is bad or to stop doing it. You could show her that you empathize and that you will help he get some help if she needs it.

She can talk to her sister about the problem of drugs and what it can lead to when it is used in inappropriate ways. Also, she can show her sister how much she cares about her sister and loves her. Expressing her emotion of sadness about her sister's drug problem would be more important than trying to stop her right away. Moreover, trying to figure out what leads her sister to start drugs would be important because everyone has different reasons to go in a bad way. Then, try to get over her addiction together. I believe that showing her sister that she understands her sister would be the most important step to do.