The most she could be charged with would be a Federal Misdemeanor, Title 18, United States Code (USC), Section 1924(This is the same thing that Petraeus was charged with: for which he received 2 years probation and a 100k fine)and she would not be allowed to run for public office. Also under 18 USC § 3282 a Grand Jury must issue a Federal indictment within five (5) years after the defendant committed the offense. Benghazi Attack occurred on September 11, 2012.
And what if a sitting president had done it?
IMHO high crimes and misdemeanors....