Going into ToM, Egwene knows Mesaana is in the Tower, but not who she is, and she has to set up an elaborate plot to find her.

So, what easy ways can we think of to expose her, in much less dangerous ways?

My first thought:

1. Bring in every Aes Sedai. Tell them they must join a circle. It could be done ina formal setting or less formal. She starts with her Ajah heads, and does it with them. Then they're told to bring in a few people they trust, and do it with them. Then just have everyone in the know pass it down and confront everyone in an orderly manner. Remember, those with stronger strengths can practically make demands of the weaker sisters. They could easily "demand" a lesser one to help. Or however they want to do it--would not be difficult to arrange for everyone to join a circle. See how much power you can pull through them. If the strength is far and away above that of a normal Aes Sedai--BAM, you've found your Forsaken--and she's in a circle with you leading!
Problems:
A. Perhaps Mesaana's strength isn't what they expect it to be? Highly doubtful, afterall. I think it'd be a safe assumption that one of the 13 Forsaken aren't shockingly very "mid-tier".
B. The weave designed to hide your strength completely, or to "falsify" your strength may be able to prevent a link from drawing more than the "falsified" amount. Nothing we have indicates it could do this--but I'm just putting it out there as a possibility.

2. Bring in every Aes Sedai. Shield them. Slash any weave that might be around them such as a Mask of Mirrors. Then, let them grab the source, and re-swear the 3 oaths. If shielded first, and then told to grab the One Power, they wouldn't have time to make the weave to invert following weaves or prevent from showing they're already holding the power.
Problems:
A. We're swearing them AGAIN? Highly annoyed and people would be very upset having to do this again.
B. Seems very similar to an assault.

Any other ways?