It may not be something that that has only happened in the past 10 years.
I’ll give my experience as an adult child who has cut contact with their elderly mother. It was more of a straw that broke the camels back type of thing.
I was brought up to believe I was not good enough, blamed and punished for things I hadn’t done. Told off for being upset or ill. Some very nasty things were said to me. Obviously I was hit as well. My sibling on the other hand was the golden child. Could do no wrong and always praised.
As an adult I have always had low self esteem. I’m not good enough. I’m too scared to stand up for myself so allow people to walk all over me. A people pleaser so I don’t get punished for doing wrong. It’s very hard to loose that mindset.
I attended special events etc as I was scared not to. Scared of my punishment but also of other peoples opinions. What type of daughter doesn’t go to their mothers birthday? It would be further proof that I am the problem child my mother always told me I was.
Last year I had my “Aha moment”. My mother did something to someone else and I saw her as the nasty person she really is. Spiteful.
I tried to make things work but once she found out what upset me the most she doubled down and did it more. The only way I can stop being treated this way is to stay away.
I know my sibling will see her differently to me. They go along with her lies and run around trying to please her. They are so used to it they don’t see it as wrong.
I’m not saying this is the case with the OP and her sisters. Just answering this question.