It’s clearly something she’s ashamed of, and also was at the time. In her favour, she stopped op. Many kids their parents don’t stop, I was one of them.
I understand your anger, but I also think you need to try to see the other side, which is what people are trying to tell you, which is there may have been more to this, pnd for example.
Simply because it didn’t make you lash out at your children does not mean it’s the same for everyone. It is likely if she had pnd she struggled to bond with you. Which could have resulted in where you are today. In addition she may have struggled to access help, resources were very different years ago.
This is not invalidating your anger, or validating what she did, I’m the last person who would ever validate someone who hit their kids, and have zero tolerance for it, as anyone who has seen my posts on this subject before, it is usually very triggering for me for obvious reasons and my instinct is to crucify the perpetrator, , but in this case it does strike me she was showing remorse at the time, and that she stopped hitting you.
This makes me think there is a mental illness element to it. Because any abused kid will tell you, in most cases when it’s just who they are, they don’t stop, not until you’re old enough to hit them back and cause them some Serious damage.
What I’m trying to say is abusers don’t change. That’s who they are. They start hitting and they don’t stop. They see nothing wrong with their behaviour deep down, or not enough wrong that they wish to stop. Your mother did See something wrong, she did wish to stop, and she did stop, which indicates possibly there was something else going on here.
For your own mental health instead of putting this down to simoly she was an abuser, which may well be the case, try to think through all elements of it.
If you can’t ask her then counselling may be the way forward.