That 4MC is on the internet at all should have a parent's knowledge and supervision.... but you, my dear busybody, cannot control their child for them. That the kid has been here 2 years without misbehaving and getting herself banned indicates to me that she is at least not an overly disruptive or malicious troll.....
Who cares.... if she gets out of line, she'll be banned, like anyone else.... If she wants adult content, there are easier and less moderated places she would have been able to find.
I gave my opinion, I stand by my opinion. You're correct it's up to the mods to care or not.