I have an incredibly toxic sister. I've done my best to befriend her or tolerate her but she's been so rude and aggressive to me that I've finally decided to cut her off. I'm at peace with my decision. Right now, due to a series of bad financial decisions on her part and a bit of bad luck, she finds herself living with my mum. The last time I went to see my mum she went out of her way to be rude, hostile, contrary, argumentative and aggressive with me. My mum is aware of this (it's gone on for years) and generally asks me to be tolerant, rise above it and put up with the abuse because 'that's what she's like'. While my sister is an adult, I think my mum holds some of the responsibility here because she's encouraged us to tolerate this behaviour for years.
Recently, my mum invited me to her house. I declined, and told her it was because I was tired of the way my sister behaved towards me and I didn't want to be around her any more. I also invited my mum to come and see me at my house. She was upset, said I was putting her in the middle and declined the invitation. I haven't heard from her for over three weeks, which is very unusual for us.
My question is, how long can the parents of adult children be reasonably held responsible for the behaviour of their children? While my sister is an adult, she's also a guest in my mother's home and I'd be mortified to host a guest who was so rude to my other guests. How irritated with my mother am I entitled to be?