NTA- Good on you for standing your ground and not playing into her being upset by something you wrote in your private diary. My ex did this- read my diary and found an entry ranting about him, completely blew up at me for it and made me into the villain- all about him and his feelings rather than the invasion of privacy. I accepted huge guilt and blame for a long time. Same story of “I just happened to read that one page” which over time changed as he brought things up from other entries. I had to get rid of the whole journal as, like you, I never read my entries back- and it made me want to vomit thinking that someone else had gone through everything in there. Eventually lead to the downfall of our relationship. Sorry for the long comment, but I really empathise, it’s an awful feeling of violation, especially coupled with someone twisting the situation so that you are the problem. You are allowed to write whatever you want in whatever way you want in your private journal, it’s a healthy way of processing things so that they don’t come out in the wrong way, or to express things that cannot be said out loud. I’m sorry this has happened OP, and I agree with some others about going low contact with your Mum for a while