Chandler was supposedly a female Starfleet lieutenant and a member of Internal Affairs. In actuality she was a hologram which was part of a simulation designed to test Julian Bashir's loyalty to the Federation.
As part of the program, she accompanied Luther Sloan (who was in reality an operative of Section 31) onto Deep Space 9. She assisted him in his investigation of Doctor Julian Bashir as a possible spy for the Dominion. Chandler escorted Bashir to various interrogations, and placed him in a holding cell when Sloan had him arrested. Bashir, outraged, said that he had lost many friends in the war. Chandler responded by agreeing, but said those friends were Jem'Hadar. (DS9: "Inquisition")