It took me over 50 years to forgive my sister. I raised two of her children because she could not due to her addictions. Three others went into foster care before the family knew what was happening. Their father got them out after a few years; he died several years ago. My sister died a year and a half ago. I did not go to the memorial. I did not go because I thought I would be a distraction; it was a time for her and her daughters to come to peace with her--which most of them had before she died. All of them were very angry that I was not there. I did what was right for me.
My sister was diagnosed bipolar long too late to have much effect in her life. She had drug and alcohol addictions. She was a very ugly drunk and referred to me frequently as "Miss Goody Two-shoes." I never bad-mouthed her to her children, but I was angry that she abandoned them for what she called "partying." I didn't understand her pain. If you don't believe you can change your life, you can't.
One of the daughter's I raised has had the same problems, and I have raised both of her children. I have spent decades pulling this daughter to safety time after time, only to finally accept that I cannot save her. She has to want to save herself and believe she can do it. It's not going to happen. I still have the youngest child with me, and I love him more than anything in the world. I am trying to not make the same mistake of not letting him face his own consequences.
I think what I'm trying to say is that only you can decide how to react to this situation in your life. Make your decision on what feels right in your heart, not on what you think others may expect of you. Your sister is responsible for her own life. You do not owe her anything. Forgiveness does little for the person being forgiven; the person it brings peace to is the forgiver. I forgave my sister some years ago. I'm not sure she ever knew it. I didn't do it for her; I did it for me. It has made me a better person.
I pray for peace in your heart.