First off you have to think about what is in the best interest of the child, your sister. Secondly, you must be prepared for the events that may possibly follow, what would your mother do? Does she know where you live?
You may need a restraining order against your mother, I suspect she would flip out and you have to keep your family safe but at the same time keep your sister safe as well. I would testify but get your affairs in order first before the bomb drops. I would say call CPS but then your sister might end up in the system.
If you feel your sister is eminent danger you can get an order from juvenile for her to be placed with you temporarily until your stepdad can get custody. You need to go to CPS and get any and all records from when they were called, there may be incidents you don't know about or remember that can be helpful in establishing a case against her. My mother was abusive to me, my brothers and my dad.
I still struggle with it as an adult I left home when I was 16 and never went back. I remember it like it was yesterday, walking on eggshells fearing setting her off, and sometimes she just felt like doing it not because she had a reason. Even as an adult I feared her, I spoke to her on the phone but never could gather the courage to go face to face.
She never apologized just said she did what she felt was right at the time. She ruined my dads and my brother lives, they will never be the same again....ever. Her abuse went beyond beating the hell out of us with a belt, she got JOY from it, especially with my dad.
Thinking about it makes me sick, he was disabled and she preyed on him, sucked the life right out of him. I hated her for taking away who he was. I am sorry you went thru that, you need to get your sister away from her before she does the same to her if she hasn't already.
Testify against your mother for sake of your sister. Your mother is not mentally stable, which means your sister will grow up the same way, especially if nobody is around.
I cant really gove you an answer,but what I can give you is a way to a solution, that is you have to find the anglde that you relate to or peaks your interest. A good paper is one that people get drawn into because it reaches them ln some way.As for me WW11 to me, I think of the holocaust and the effect it had on the survivors, their families and those who stood by and did nothing until it was too late.