meaning he was essentially calling her a trainee.

I will do nothing without proof. I will not be goaded, this time. She was not the Egwene he had grown up with; she had become part of the Tower since Moiraine sent her there. Moiraine again. Always Moiraine. Sometimes he wished he were rid of Moiraine. Only sometimes?

He concentrated on her. "What do you want of me?" His voice sounded flat and cold to his own ears. The Power stormed inside him. Egwene had told him that for a woman, touching saidar, the female half of the Source, was an embrace; for a man, always, it was a war without mercy. "And don't mention wagons again, little sister. I usually find out what you mean to do long after it is done."

The Aes Sedai frowned at him, and no wonder. She was surely not used to being addressed so, not by any man, even the Dragon Reborn. He had no idea himself where "little sister" had come from; sometimes of late words seemed to pop into his head. A touch of madness, perhaps. Some nights he lay awake till the small hours, worrying about that. Inside the Void, it seemed someone else's worry.

--Rhuidean, The Fires of Heaven