Since this girl is a legal adult, if she is "missing" by her own choosing and LE know it, they (LE) are under no legal obligation to tell the public anything. Although, in most cases, as a simple courtesy to the public, when someone does go missing by their own choosing and LE has previously asked the public for assistance, they will issue a short statement to the affect of "has been located and is safe - wishes no contact".
As with many "missing" cases, the longer it goes on the more details come out that should have come out right away, but didn't (for a variety of reasons). I have no clear direction on this - whether she's met with foul play, took off on her own, or a combination of both.