It might have been, but not necessarily. The truth is that no such "traitor" is actually necessary. Remember that Cadsuane was foolish enough to keep the bracelet and the access key in a box in her _room_. That would be the first place anyone would look ofcourse, so there was no need for Sorilea or anyone to tell the shadow.

As for the question of how the wards protecting the box were bypassed, Sanderson actually told us:



If Sorilea had revealed to the Shadow how to unravel the wards, then the "rarely known weaves" would not have been required. No, I think Elza was taught some obscure AoL techniques on breaking through wards, and she went to Cadsuanes room (the obvious place) and used those weaves to get the bracelet.



IF it was her, then she is obviously working for the shadow since if she was involved she must have informed Shaidar Haran.



Elza broke the weaves thanks to whatever SH taught her.



The question has been debated. It has been suggested that the DO wanted Rand to have the access key, so that when he went mad from using TP he would do mad things with it. Other possibility is that Elza was so panicked by meeting SH that she simply neglected to pick it up.