What Leane did, and which Egwene regretted not doing, was make the weave for Cuendillar, then inverting it, and also hiding her ability. Leane made the weave too far away to be detected, and then inverted it to avoid detection when she got close.

Now, Egwene wouldn't possibly hide her ability during the height of battle. It just made no sense. And once the Sharans came, and weaving, even the one to hide your ability, would have been detected. She had no way to sneak out without detection.

But that scene was stupid anyway. She had enough strength to cause a major distraction, and while they were dealing with it, she could have gated out of there. As usual, Brandon had to invent an artificial situation to make things "interesting", then have Egwene display completely secret abilities with knives.