How do you know when it's time to get your sister out of your life?

My sister is the most hateful, defensive, sensitive, mean person I've ever known. I see no reason to have a relationship with her because she causes me so much anguish and mental distress.

I've tried having a relationship with her for decades. Every time, the same BS happens. I think it's time to sever ties with her. However, my mom disagrees and thinks I should put up with my toxic sister's behavior because, after all, she's my sister. I told her I wouldn't accept ANYONE in my life who treated me like that. She simply doesn't understand. The thing is that my sister treats her like s$#te and she appears to accept it.

Is this a case where I really should keep my sister in my life and forgive her behavior? I don't understand why I should be treated more poorly by my sister than a regular person off the street or any of my friends.