Please don't call a 17-year old person a child. It's not as if on the night between 17 years, 11 months and 30 days, and 18 years humans undergo some sort of metamorphosis.
Yes I agree, which is probably why we should treat 18-year olds more as children than adults (although obviously they are in-between the two). Brains continue to develop to the age of about 25.
The brain does not fully develop until 25, 18 is simply one of many thresholds where we've decided (in the US) to start officially transitioning children into adulthood. Others include 14-16 (driving), 21 (drinking), and 25 (car rental).
So if 17 can't be called a child, what can? You have to draw the completely arbitrary like somewhere. Do you chose the legal 18 (in the US)? The Hebrew 13? Some other metric?
Brains continue to develop through our whole lives.
The study that appeared to show them stopping development at 25 did not have any participants older than 25.
The difference between an 18-year-old and a 24-year-old is much more comparable to the difference between a 24-year-old and a 30-year-old.
We should be treating teenagers much more as adults-in-training, in the sense of meaningfully giving them the tools to succeed as adults, rather than treating them like pure innocent children who must be sheltered from absolutely everything hard, scary, or taboo.
However, as it stands we generally do not do that—hence, in this case, she was indeed a child, and should have been given compassion, better tools, and better chances, not locked up.
Please don't call a 17-year old person a child. It's not as if on the night between 17 years, 11 months and 30 days, and 18 years humans undergo some sort of metamorphosis.