If T'Rul was something more than a technician, then she'd have to be someone highly trusted by her superiors. She has to balance revealing enough info to the Feds that she seems cooperative, but not so much that she seems too friendly with the enemy. She has to serve the Empire's interests without being too suspicious about doing so, both to Starfleet and to the Empire.
At any rate, I don't see why T'Rul would be returned to DS9 as a Cretak-type liasion. That's an incredible jump in position. T'Rul was a mid-career officer in the military. Cretak was a Senator. Maybe T'Rul could've been an aide to Cretak.