I am so sorry for what happened to you. I know it may not mean much from an internet stranger, but what happened was wrong and it was wrong of your mother to not do something about the abuse.
Thanks for sharing your story and for another perspective behind why thin/average girls might say they are fat even when they aren’t — I do appreciate it.
It’s true — your beliefs define you. That’s why my word of the year last year was “Believe” actually — I was working to correct false beliefs I had in my life that were hurting me.
I hope you are seeking a way to learn to believe that you have worth, that you are lovable, that you are valuable. Because you are.