Seriously though, in a situation like that, how do you explain to the kid it's bad otherwise? Ground an 11 year old? That just makes em angry...and sneakier. Stern talking to? That went out the window already seeing as the parent was so on top of her kid to begin with. Having cut this girl's hair, just a ponytail mind you, she wasn't shaved bald, shows the young girl that it wasn't nice, it is demoralizing and embarassing. Thankfully, her hair will grow back, and she will never cut some little girls hair off again.
Also, she's 11 years old. Right and wrong should be established by now, consequences for actions are necessary. Also, she sure as shit knew what she was doing. 6 or 7 I could understand this as excessive, 9 maybe, but after 10 years old you have to be responsible for your actions. Murder is still a little out there as the concept of taking a life is still a bit extreme, but causing pain and or suffering to anyone at that point is something we would consciously be aware of. The "just a kid" excuse has is a bit late.