I’m so, so sorry your mother has been so ill for so long. You didn’t indicate when this started. But you did provide enough information for me to suggest a thorough evaluation by both a medical doctor and a psychiatrist. It could be that her medical condition is contributing to this behavior. It’s also possible that she has a significant mental illness that shows up periodically. I can’t make a diagnosis on the basis of only a short letter, of course. But I can tell you that since she has good periods as well as bad ones, we might want to look at a bipolar diagnosis.
It’s up to your dad and the rest of the family (grandmother and aunts) to insist that she get evaluated. She is not likely to listen to you as she sees you as her child. I do suggest that your father look into what is involved in your state for her to be involuntarily signed in to a psychiatric hospital if she again becomes irrational and physically abusive. It may be the only way she gets the help she needs.
I wish you all well,