The cop acted inappropriately, unfortunately, on this incident.  All be it, with the right intentions.  What he was attempting to do was rule out any discrepancies on the victims part in the accident.  But, she was right that he needed a warrant from an unconscious party who did not willingly allow evidence that could incriminate himself somehow.  Had the person been a suspect and under arrest with a serious injury accident, there is not consideration for a warrant in taking blood.  Implied Consent covers that aspect and he would have been allowed to take the blood without a warrant.  Somehow he confuses  the person that is a victim as a suspect, I guess.  Lastly, resorting to force instead of the rule of law never works in your favor in these situation.  There are legal experts, both in law enforcement, the judicial system and the hospital that would have determined what the legal aspects were and are.