Hi Tangerinefeathers, your sister sounds awful. Did she thrive on guiding you to, well, f*ck up?
on your behalf...and a way good thumbs up on the disconnection. 
Hi Stardust, I hope you had a lovely holiday. Don't beat yourself up for making contact. Just think of it as a slip up. You wrote previously that you know it is her and not you. It isn't you, it is her. You are cool, she is not. She is awful, you are together. 
Your sister is an adult. She doesn't need you and you don't need her; she isn't responsible for you and you are not responsible for her. Yes?
You are burned out and used up by her. It is time to step away. Imho, for me anyway, it was like thinking about sister was a habit, a bad habit...then it somehow snowballed into the obsessive addiction thought process. Sisters' actions and interactions with us have been all about them (and it didn't help that with your sister, it was all negative) and that has in a way trained us to, wired us to, brainwashed us to think about them consciously or subconsciously.
I finally came to the point of being tired of thinking about her. (A first step was realizing how much I had been venting to dh and stopped that-he was sick of hearing it.) Then a sort of revelation hit me that I was still making my life about her (even though I had not seen her in years) by continuing to think about her. My life is not about her, my life is about me. That is my new mantra. My life is about me and I need to, and it is ok to, think about me, and not her.
This does take time, Stardust. It is retraining your brain to think differently. After dealing with toxic people for so long, thinking of ourselves, putting ourselves first, is a change of thinking.
Sorry this is so long, hope it can help some.