My impression of that whole event was that it was more than a Lord of the Flies type scenario. Gen. Whats_her_name was quoted in one of the reports that she was told by "lower ranking CIA" that she was not allowed to walk the halls of the prison she was in charge of. I really find it hard to believe that these prisoners were dressed and undressed as different officers and interrogators came through and that no one knew what was going on.
My take is that this private was just following the lead and absence of lead from above and all around her.