How do you let go of a toxic family member?

I recently visited my family for the holidays and stayed with my sister for nine days. My sister has always been my best friend. There for me and took care of me since I was an infant as my mother was absent. On the first day, on the way to her house from the airport, she told me that she has a very rare blood cancer for which there is no treatment. She could die in two weeks or twenty years. No one knows. I decided right then and there that I would do everything I could to be there for her and that I would do everything she wanted to do during my visit. (Unlike visits in the past when I was so depressed I didn’t want to do anything).
But she had other ideas. She spent the entire nine days being mean and cruel to me and bullying me about any and every interaction we had or that I had with other people. From hating the smell of my toothpaste to the way I spoke to my mother. Nothing I could do was ever right. She accused me of calling her stupid at least five times a day. She called me passive aggressive and said that I mumble. None of that was true. She’s the smartest person I know. I’m a loving and kind woman and mostly people say that I talk too loud because I’m partially deaf. No need to elaborate, you get the picture.
I realize that she is probably sad and angry about a lot of things. I know she is capable of loving kindness because I watched her treat her husband that way the entire time. She’s always been a bully and capable of being mean and cruel but it was rarely directed at me.
So the point of this massive rambling is how to let her go. I was abused and bullied by the rest of my family for my entire life. I’ve learned that I don’t have to tolerate abuse. I tried to talk to her but she continued the abuse and refused to acknowledge that she was behaving in any way that was abnormal or inappropriate.
I know that everyone dies sometime, and that absolutely nothing excuses abusive behavior. At least that’s what I believe. So I have to let her go. I have to distance myself from her to avoid having my self esteem go down the toilet like it did when I was visiting.
It’s breaking my heart. I can’t even face it without feeling as though I’ll break down and never recover. I need help and support. I have some people who do that as well as they can, but no one who truly understands. I’m reaching out to all of you in the hope that someone out there has experienced something similar and has a little advice about any of it.
Thanks for listening.