Shexis probably blocking something Trump wanted released Tru p said would fire her so she resigned, knowing Trump can’t get a loyalist in place in time to do the relase.
She has been preventing the left and foreigners from obtaining information and evidence pertaining to the interrogations of the likes of Binalshibh, blocking prosecution by the left of interrogators in the GWOT.
That in turn may havr to do with the intense desire to cover up anything about Iran and terrorism attacks on the US.