So we have a To'raken that has a captured AS on it along with a couple of Dammae/Sul'dam. They attack the Tower. Is Egwene supposed to do nothing? Let it throw fireballs etc against her and the Tower? That's not an atrocity, that's just defense. The difference between that and Graendal is that Graendal and her minions were not activly attacking Rand and his forces. In addition, was there any reliable way to detect which To'raken had captured AS aboard and which didn't?
Finally, the captured AS would be enslaved and forced to reveal information, not only Traveling but also all kinds of other information that the Seanchan would use to subjugate the WT. Maybe being collared is "a fate worse than death" Egwene certainly thinks so, maybe it isn't, who is to know? However reducing the knowledge the Seanchan can get of the WT is of utmost importance.

NaCl(it's called collateral damage)H2O