Either the Binder works on the soul or the connection to the Power. Either way, the most important thing is the outcome - the skin is tightened and an effect very similar to (a literally skin deep) powerful Compulsion is laid on the channeler. As I noted, being a channeler and holding the Power already protects you from certain things, such as Compulsion, aging and illnesses, while a non-channeler is afflicted with these ailments. Even if we don't know how or why this is the case, all we need to know is that the Binder requires some element present in channelers but not non-channelers to work. You can swap in connection to the Source, channeling soul or brain difference as needed, but the inherent logic remains the same.

If the Binder did work on the soul, perhaps Mesaana is protected because hers is given to the Dark One or perhaps she made a mindtrap for herself to house her soul temporarily.



But we already know that there are many channeling abilities that don't require holding the Source, one of which is the manipulation of your link/connection to the Power to escape a Shield. Note I never said Mesaana had to hold the Power while swearing - all I said was that she used the increased capacity of a Link to Shield herself from the full effects of the Binder. She could actually invert her weaves hiding her ability to channel and her hold on the Source appearing as if she didn't touch the Power with noone being the wiser - Egwene knows about inverting weaves and hiding your channeling, but not how to detect if someone else is doing the same.

Mesaana wouldn't need to trust her fate to the Black Ajah - if she was the leader, she would actually have them at her mercy, since it would be up to her when to dissolve the Link. And this fits in with the possible need to defend herself if her subterfuge was discovered - with access to such a Link, she could overwhelm many Sisters during her escape attempt if her plan went awry.