Did Egwene have any reason to suspect that any of them knew Travelling? Even if she did, it's a big assumption to think she could kill ALL of the raken - for all she knew, by the time she entered the battle, Elaida had already been captured.

In terms of the AS becoming damane - they are still held by the Oaths, plus they, well, pretty much suck at combat. If they heal Seanchan soldiers, I don't think that's such a big deal. And in the timeframe before T'G (I doubt it's more than a month, or two at most) there's little chance that the captive AS would be completely broken to the point they couldn't be "reclaimed" back into the WT. I'd actually go as far as saying their emprisonment could be GOOD for the light - it's not unreasonable to think that Rand and Tuon will form some kind of alliance before the LB, and when they do, they'll have a few hundred extra trained damane who have learned combat weaves and whose Oaths still allow them to kill Shadowspawn. Which, I think you'll agree, is better than them sitting in the tower studying poetry. Their capture doesn't reflect well on Egwene, but her compassion/pity in sparing their lives might make a big difference in the end.