I'd say most of my trauma stems from my issues during early adolescence, my mother's complete lack of response to an obvious problem and not getting the support I needed from her.
Early adolescence was when my mental health issues first appeared. I had developed severe depression, horrible anxiety, and while I didn't have a name for it at the time, I was also suffering from deep gender dysphoria as well. I was having screaming, sobbing breakdowns multiple times a week. I was cutting, punching and biting myself on a regular basis. I hated myself and I wanted to die. I would regularly go to her and tell her how everything was wrong, that I was hurting myself, how awful I felt, and that I wanted nothing more than to just die. She knew about everything, and there was a clear and dire need for intervention.
So naturally, she decided it was all just silly teen angst and did nothing. At one point I even specifically begged her to get me help and she still did nothing about it. Then when I aged out of being a teenager, I was obviously still racked with bad mental health issues and doing nothing with my life as a result. She was frustrated and for some reason surprised that I hadn't just grown out of it.
The time I came out to her as transgender didn't go very well, either. Being that I lived under her influence and was unaware of how messed up as a parent she actually was, I still loved her and had a close relationship with her in spite of everything. I trusted her and I felt that I had no reason to expect anything other than acceptance and support. But she wasn't supportive, and said a number of horrible things that will stick with me forever. I went through so much anguish pleading and waiting for acceptance from her that was never going to come.
She did finally get me into mental health treatment as a young adult, but to me it felt like it was too late by then. Essential time and development as a teenager was wasted and lost, and I still feel like I'm not a complete person and something about me is fundamentally broken as a result. She also strictly wanted my treatment to just be about dealing with the depression and anxiety, deciding that I should put being trans to the side and ignore it. Which is something that I was completely unable to do, so not addressing the third core issue ultimately meant that the therapy and pills weren't nearly as effective as they could have been.