You're absolutely correct. There is a very real reason that the military is in our high schools recruiting children. It's because they aren't capable of understanding the consequences of their actions. And the fact that the recruiters are allowed to lie?? It's worse to me than what Lily is doing with her body. At least she can stop at any time. Once you're government property you have very few choices. My childrens' father signed up for the military without talking to me about it when he was 19 because I was pregnant and he saw that as a way to "take care of us". However, after serving in Iraq he came home damaged beyond repair. I'm afraid Lily doesn't know that she's doing the same thing to herself. If she were cutting, we'd see it as the self harm cry for help that it is but instead we have to wonder if she's actually enjoying herself. Spoiler alert, she's not. It's self harm with a prettier wrapping.
Each person's brain is fully developed at a different age which is why it's so difficult to judge actions based on a chronological age. Maybe her brain is fully developed, maybe it's not. But I'm sad for her. I wouldn't be surprised to learn that she's acting out because she was molested or raped as a child - possibly even before she has memory of it. I acted out in similar ways (even if not so dramatic), so I'm speaking from personal experience here.