A group of assassins is sent to wreak havoc in the White Tower after the raid ends.

We see one of them during the last stages of the battle outside the tower, true, but not hundreds of miles away like Perrin, but merely a few steps away, probably preparing to enter the tower just like Siuan's group is about to. (this seems pretty obvious, wouldn't you say?)

So they are in the tower or shortly will be (in a few hours at most) and will start targeting prominent figures.

Would they try to kill Egwene? She was the leader of the defense so she is in all likelihood their no. 1 target. If they don't recognize her on sight listening to a few tower residents will give them all the direction they need.