Egwene knew she could stop weaves. She was just slack jawed about the balefire because, as she said, the OP was dominating her thought too much. BF is an insanely powerful weave. Seeing it stopped for the first time awed her. But, like she says later, it isn't what Perrin did but that he was the one doing it that surprised her.

She didn't really learn anything new. She just got her perspective set straight, which had become somewhat wonky after the months spent with the AS and away from the WO.