Looking into the situation I think you may have it backward. I do not know for sure though. She appears to be born female, transitioning to male. Very possible that taking testosterone could have caused her already fragile mental state to SNAP!

Estrogen would make a HIM hide and cry... unless they suddenly went off estrogen and having natural testosterone retake over the body, that might make a male born, transitioning to female person SNAP. I do not think that is what happened in this case

I read that the school was PRO children transitioning / pro lgbt+, and she went to that school. She had writings that she was ANTI children transitioning. Maybe she was a tomboy as a kid and convinced that she was trans and then made permanent life changing body alterations from the guidance of people from that school. Maybe ruined her ability to ever have kids,... (Wonder if the kids she killed were transitioning and somehow she thought she was saving them a life of misery like hers???)

That is my theory so far from what has been released in the news and dug up by others here and on different sites.