Well, an argument could be made she didn't want to tip her hand once she knew Moiraine had found, or was close to finding, Rand; the one big advantage they had between Winternight and the fall of the Stone was that they knew who the Dragon was (or were at least fairly certain they did) while the BA simply knew he was out there somewhere. It's rather surprising the Forsaken didn't tell them (though they were flashing their faces as early as TGHs prologue), or maybe it's not since the BA is such an erratic and overly ambitious loose cannon throughout the series. Ultimately, however, Siuan should've realized that the BA knowing the Dragon had been Reborn almost as soon as she and Moiraine did meant they'd come to precisely the conclusion most of them did even before the Stone: That the otherwise unremarkable backwoods shepherd boy who just happens to be in his late teens, looks like he stepped out of the Waste, is surrounded by bizarre events and inexplicably holds the fascination of both the Amyrlin and her pillow friend is PROBABLY the Dragon Reborn. For all her pride at having kept back Rands identity under torture, the fact is most of the people inclined to press her for that bit of data knew before she did. She concealed little, if anything, and rather than averting suspicion, she increased it.

It's amusing that while there seems to be a consensus that Egwene has inherited Latras role, if not her soul, it's only deepened rather than resolved the debate about both womens worth. From what LTT says through Rand it's not clear the womens involvement would have prevented the Taint, and might have made it worse by infecting every subsquent channeler with it (on the other hand, with the greater ability and strength available in a 72 person link perhaps the Companions could've accomplished their task and been done before the DO had the CHANCE to respond). What we do know is that a "re-Taint" would hardly catch Rand by surprise now, and he's working hard on an alternative even if he hasn't found it yet. Nonetheless, Egwene stands ready and eager to oppose him on anything not her idea despite his possession of strength, ability, knowledge and experience that dwarfs hers. Not that Egwene has a viable alternative (Latra at least had that much), she's just rejecting unheard the only one on the table. Never mind that it's coming from the man prophecied for three millennia as the Lights champion and only hope at the Last Battle who, oh, yeah, just happens to be the reincarnation of the greatest channeler who ever lived, who forged the Seals in the first place. I seem to recall Jordan specifically saying something that rules out Egwene as Latra Reborn (I want to say Latra hasn't BEEN Reborn), which argues ta'veren aren't the only ones the Pattern spins out to play a role. After all, had Egwene not been able or willing to oppose anything and everything Rand said, Elaida would've been equally happy to do so (it should give Egwene pause that despite wanting a break from Elaidas regime her plan for "dealing with" the Dragon is only nominally different). Makes you wonder who would have gone to the Waste if Tigraine hadn't felt like it.