Siuans two decades of manipulative scheming made her Amyrlin and thereby gave Moiraine the resources and latitude to find, protect and prepare Rand for his destiny, but also created the enduring legacy of suspicion and betrayal that deposed and stilled her. That might be excused as a necessary evil to ensure the Dragon reaches the Last Battle (she seems to justified it thus to herself), except that had she not been so consistently devious and tight lipped about all her activities the Sitters would not have been so receptive to whispers against her, and had she involved anyone but Moiraine (even Leanne, who was pointedly excluded) she might have had some whisper herself about what was brewing. Instead, Elaida was able to buttonhole Alviarin without her notice and the two of them to muster most of the Hall against the Amyrlin under her very nose. Against that backdrop Egwenes treatment of Gawyn is par for the course; when SOP is "trust no one; they're all too stupid/wicked to merit trust" it's no surprise her lover is lumped into the category along with her childhood friends, allies and mentor. Egwene plays her own game, and plays it very well, but everyone we've seen play that game eventually and dramatically LOST.

Actually, Siuan did want to involve other people. Moiriane was the one who put her foot down and said it would have to be just the two of them. Thank the Creator for that, because the first person Siuan wanted to turn to was Sheriam!

They really had no way back then to know who was Black Ajah, and they were very wise to shut up.

And while Siuan's silence did lead to her downfall, its a small price to pay compared to the alternatives. Even if all the women they involved in their plan turned out to be trustworthy, it would have meant a lot more Aes Sedai around Rand.

As for Merrilor breaking Egwene... I'd just re-read the whole Latra Pose vs. Lews Therin situation. Neither broke the other, and in the end, both played their part to save the world. RJ was very clearly setting up Egwene to be the Third Age's Latra Pose. The reason she came across so unevenly in ToM is because these were all scenes Jordan had less to do with than the Egwene scenes in tGS. Brandon just botched the characterization completely.