I'm sorry you are dealing with this issue. The thing is, you can't control what she chooses to do, so you have to do what is best for your own peace of mind and well-being. Many times, we have to remove toxic people from our lives, even if they are family members. You are right that confronting her about her abuse of pills won't make any difference in what she chooses to do.
It sounds like you already have little contact with her, so if you can continue the distant relationship you currently have without it upsetting you, then fine. If talking with her at all keeps you upset, then maybe you should consider no contact whatsoever. Again, the only control you have is over your own well-being, so you must decide what you are able to live with.