Ok - I REALLY think she needs a computer break for a long while.
First, it kind of goes without saying that most of what you read on the internet should be considered out right lies.
Second, it disturbs me (and probably your daughter too) that she fell so hard for this cock and bull story.
Third, is she more upset he WAS going to try to meet up with her or that he's NOT going to meet up with her?
Fourth, starving yourself to death (or threatening to) over an imaginary person at best or a close shave with some possible online pervert is just excessive/depressive, and she REALLY could use some counseling over this.
What should you do? -
She needs to be off the computer except for school work - block social networking sites.
She needs some counseling to deal with her depression (and why she got so emotionally involved over this).
She needs to become involved in some activities where she meets real people to become involved with - sports, crafts, volunteer work, get a job, baby sit, walk dogs, etc.
Don't call her foolish, just tell her you love her and are alarmed at how this whole thing is playing out and you want to make sure she gets some help in how to deal with it.