Hello, blacknwhite. I read your story several times, mulling it over in my mind. I feel the fury, indignation, desolation, pain and confusion. You are correct in saying that the tumor, autoimmune disorder, and panic attacks are the result of having to bury and hide your outrage all these years and that "she" is still doing damage to you.
To heal, you need to cleanse yourself from all this dark, damaging energy that you carry. It might sound counter-intuitive but you have to start by trying to understand her, seeing things from her perspective, even if only briefly. I will help you, but you must hear me out. I'm not making excuses for her behavior at all, but trying to offer you some understanding so you can let go of the anger towards her.
It seems that you hope beyond hope that she will admit her mistakes. But the truth is that, from her viewpoint, she did not make any. She felt she had good reason to discipline you, that she was doing what a good mother was supposed to do with an unruly daughter. She was trying to mold you into the daughter she thought you were supposed to be. NOT true but this is her view.
You have a strong, smart and independent spirit. In some cultures, that is not a good thing for a daughter to have. She felt she had to beat you to keep you in your place. On top of that, your mother bore a mentally disabled child and had much guilt about it. The anguish, guilt and stress were taken out on you, the healthy child.
Suffering from chronic beatings leaves deep psychological scars in a human psyche, and it is a testament to your inner strength that you emerged as healthy-minded as you have. Most sociopaths experienced child abuse. Of course, you still must deal with the memories, panic attacks and even physical manifestations of all that (autoimmune disorder, tumor). But you are smart enough to have gotten yourself out of the country and away from your family. You earned a college degree and have been able to take care of yourself. Good for you!
Keep going. The way to save your life is to keep growing forward, create new memories, new experiences, new joys. Looking into your past will not change the past. Your mother will not change now. You don't need your mother to admit anything in order for you to heal and move forward.
She wasn't the mother you wanted or needed back then. The good news is that you don't need a mother now. Revel in your freedom as an educated, liberated adult woman. Explore your power and your world. Don't look back until you are strong enough to do so without weakness or pain. Learn to forgive your mother because she was trapped by the worst of antiquated cultural practices, superstition, and ignorance. She is so unaware. Forgiveness is hard, to be sure. A mother is expected to give love and nurturing, and she gave you pain and cruelty. Can you come to the point of feeling at least pity towards her? She may have been raised with constant beatings herself. By forgiving her, you take away her power over you.
Because of your culture, I can understand the filial duty thing so send an upbeat letter with a little money now and then. Don't give them a return address until you are ready for interaction. You'll know you're ready when you no longer feel so angry or vulnerable to manipulation.