The teenage girl stood in her driveway in fuzzy slippers and a black coat pulled tight like a security blanket. She wiped at tears.   Her parents had called 9-1-1 because they didn't know where else to turn. They had discovered disturbing videos on social media of their daughter talking about drug use and suicide. Just four days earlier she had celebrated her 16th birthday. Now two police officers said she needed an immediate emergency mental health evaluation.