Egwene's reasoning seems to be that if Rand sees all the armies of the light arranged against him he will come to his senses and abandone his mad plan.

Personally I think that Rand simply used Egwene and the Aes Sedai to do all the work in assembling the armies exactly where he wants them. Why go to all the bother with meeting with all the leaders, writing them letters organising gateways for them to bring their soliders if you can get Egwene and co to do it for you?

At the end of the day what are the AS and the solidiers going to do if Rand does not change his mind? Lock him up, kill him? If they do who is going to take the long walk down SG to chat to the Dark One about the end of the world? None of them you can be sure.