I always love that people are so trusting of their children.
I have spent my life assuming my kids are the ones in the wrong and that they would always do the worst thing. I find this a great place to start, then you're never disappointed
Seriously though , it's only in the last year or so that tweeting and social mediating (if you will) have attracted such attention. I think they've changed the law slightly recently so that it wasn't necessarily such a big deal if somebody said something albeit in public to another via facebook/twitter. Otherwise, I'm afraid that the courts would become very congested with crimes relating to the iternet.
As a consequence of some high profile cases, like the man who was refused access to the USA because he said something on twitter about hating California or some such nonsense, has at least brought people's attention to the fact that if you put something in writing on the itnernet it is there ad infinitum, and everybody can take offence ad infinitum. I expect this girl when she did her tweeting had no idea somebody would dredge them up some years later.
I'm not excusing what she said/wrote (I have no idea, actually, nor do I want to know), but I have seen some outrageous things written by adults on facebook and twitter, and wonder how they get away with them, it's not all that surprising that this girl has done similar things.
I agree with Mike, what a complete waste of a time creating a job like this for a 17 year old.