The real key here is for you to understand that:
you have every right to feel angry, and it is not your decision to make. You can't control her actions nor what she has done. The three C's hit the nail on the head.
I have grappled with these issues myself, and essentially my relationship with my mother is almost non existent unless she is trying to hit me up for money or is on cocaine and being a chatty Kathy and calls me to check in.
An important thing you must know is that often times this behaviour can lead to you repeating the same exact behavior yourself. I along with other co-dependents I know have lead ourselves down the same path of destruction. I am a life long co-dependent as my mom has regularily been abusing drugs since my earliest memories, and I am especially worried that your sister could walk down the same path since that is all she has ever known according to your first post. The array of emotions you go through can be mind numbing between: Worrying for their safety, Resentment, anger, a feeling of abandonment, and just generally feeling unloved. It took me a very long time to realize how living in a constant state of lying, fearing family members taking me away, them acting is if they are the victims despite and the whole world is out to get them, and the unfair judgement that people held towards me over her behavior is what was behind a lot of my low self esteem and personal addiction issues.
I am not trying to make this about myself but rather would like to say that you are not alone. It just seems as we get older these issues start to effect us more and more as we understand them. So i have a few questions for you (sorry if i missed them but there was ALOT said)
#1- Do you engage in any addictive type activities such as drinking drugs etc.
#2- Does your sister do alright in school, and how does she manage the problem?
The only reason I ask is because people in our position need to be extra careful, it is very easy to repeat the cycle, and I would hate to see you walk down the road that so many of us have.