Changes associated with puberty could also be a factor.
Totally agree.
My daughter went through some personality changes when she hit 11-12, she became more aggressive, argumentative, not listening and on. When she told me she had tried to cut herself and felt she didn't want to be here anymore, I took her to the family doc who referred her to a youth psychiatrist. They diagnosed her with ADHD and put her on medication, it worked wonders, and my happy well-behaved daughter was back. Yet, she didn't 'like how it made her feel' and wouldn't take the medication anymore. I could not and would not force her and to be completely honest, it has been hell for the past 6 years. She is highly reactive to anything she does not like or if things don't go her way. We had holes in her bedroom wall where she basically kicked the crap out of it because we told her to get off the video games as it was 2 hours past bedtime, she has destroyed her relationship with her younger brother who is also 9, the same as Zander and so much more. She ran away last October and refuses to come home, she turns 18 next week, and because she was 17 at the time, the police and children's aid cannot do anything. I see her occasionally now, and she has been thrown out of several friends' houses for lying and causing conflict within the families.
This case really REALLY hit hard on me as I saw the anger and hatred my daughter felt towards her younger brother, who, once upon a time, she doted on and wanted to be with all of the time. I feel this could have easily been my family.
This 12-year-old girl has so much weight on her shoulders now and will for the rest of her life, regardless of treatment programs, being locked up or not. I know if I was the mother, I do not know if I would be so forgiving, let alone even think of letting her near my other child.
Edited to add: I am not judging anyone, I'm just stating my own opinion. There has been mention of non-psych drugs being to blame and I doubt we will ever know which drug it is