Just as a disclaimer: My advice on this particular topic isn't gospel and I don't expect everybody to follow it. I'm just going to base my advice off of my personal experience, and I'm sure everyone else's experience (dealing with family or friends) is similar or really different.

From what I've learned in having to deal with these kinds of people (such as your sister), I've learned that giving them the benefit of the doubt, expecting them to change, can shave off years of your life. Even if they do somehow manage to change, a lot of times they will just go back to the way they were before. I realized that there was a point in which I shouldn't feel guilty about not wanting to sacrifice my time, energy, and the quality of my life to address the concerns of those that consistently ruin it, and I'm not willing to give that up on the 5% chance they change, which could take years to happen and with no guarantee they will keep their behaviour changed.

The time and mental energy people spend dealing with shit that others cause (which indirectly affects them) is time they will never get back. There comes a point where you have to decide whether it is worth it.

The simple fact is this: Some people are just too far gone. Your sister is one of those people. In your sister's case, based on what you've written, it's not worth it. Don't get involved and distance yourself from her as much as you can. She will only drag you down, just like she did with your parents.