I started following this story last night after Obama's speech, as it blew up on Twitter. I also followed it this morning after the girl deleted her twitter account and made it on a ton of sites across the internet.
Follow up from a supposed friend on twitter said the girl and her family started receiving death threats almost immediately after she posted the comment. People called her job, school, the police, her family members, friends she followed on twitter and facebook (also gone). It was a little crazy. While these comments have no place on the internet, or in public in general, I think threatening her life is going about this in the wrong way. It's a reality check for a 16 year old who thought she wouldn't get in trouble for what she said, that what she said wasn't a big deal. Again, it's a felony, something people seem to not realize. It's not your 1st amendment right, it could be seen as a legitimate threat. Presidents have been murdered and shot at by "nice people".
http://www.usatoday.com/news/nation/story/2012-09-07/obama-hate-tweet/57691144/1