If you really want to know what happened, here it is. An older Doc once told me, "We have checks in place in medicine and bad things can't happen without multiple mistakes being made. Even so it happens and when it does it isn't 'One persons fault' but multiple failures." In this case the intern told the nurse over the phone to give the agitated patient more Demerol to calm her down. There are at least two mistakes here. 1) the intern should have known better than to give the oder 2) the nurse should have known better than to give the medicine to the patient. The intern probably should have gone to evaluate the patient. The ER probably should have insisted on a patient that was that ill go to a Unit bed instead of the floor and the ER doc should have known better than to start this mess by giving Demerol for agitation. The upper level resident should have been keeping a closer eye on an intern that was this clueless. The charge nurse should have been keeping a closer eye on a nurse that was his clueless. I could just go on and on here but I think you get the point.
Oh, what a scary set of events! I can't see how there is any way to protect yourself from something like this happening to you or a loved one. In situations like this we tend to put our complete faith in the medical professionals. The family of this young girl are probably constantly tortured by the "what ifs". If any one of the factors that you mentioned had been done differently, this person might still be alive. Tragic.