Theoryland of the Wheel of Time

On the second answer: RJ indicated in Sweden in 1995 that he does use a 21-graded scale to keep track of channeler strength.

The first answer appears to be an Aes Sedai answer (avoiding the question). The real answer (at least, the answer that is consistent with the rest of the books) is that RJ probably used a bit of hyperbole in the scene where Mat was Healed in The Dragon Reborn (or rather, Nynaeve did, and she even caught herself...but RJ wrote it in such a way that left room for doubt whether she was amazed at her arrogance or at her potential strength).

The woman with the shielding talent, at least as far as we were shown in A Crown of Swords, was in the Kin (Berowin), and not one of those holding Nynaeve when they went after the Bowl (Falion, who got away, and Ispan, whom they captured). They were linked, and they waited until Elayne went upstairs with most of the Kin, then caught Nynaeve off-guard while she wasn't already holding the Power, and they (rightly) believed the remaining Kin wouldn't interfere. (Erica noted when I interrogated her about this report that these were all quick questions which he answered while signing books, so he was probably too distracted to explain properly—all indications are that he truly enjoyed explaining such things when he had the leisure to do so, and that he also would have gladly admitted to the hyperbole so long as he had time to address the rest.)

I think one of RJ's main points in that scene was that Mat, not being able to see the weaves, wouldn't have any idea what was going on, and therefore neither should we, really. RJ even called our attention to this phenomenon in the battle between Moghedien and Nynaeve at the end of The Shadow Rising:

"A man who came in then, or any woman unable to channel, would have seen only two women facing each other across the white silk rope from a distance of less than ten feet. Two women staring at one another in a vast hall full of strange things. They would have seen nothing to say it was a duel. No leaping about and hacking with swords as men would do, nothing smashed or broken. Just two women standing there. But a duel all the same, and maybe to the death."

The scene in A Crown of Swords was a way of exploring that phenomenon. Presumably Nynaeve was strong enough to break the shield, but it was close enough that it came to a fight much like the Moghedien fight. Meanwhile, Nynaeve says aloud that Falion and Ispan are linked, and she chastises the Kin for not helping her. That tells us all we need to know.