If it were only that, it would make sense. But the loyalist Sitters weren't all invited, and the Rebels weren't all present. So it clearly wasn't just about staving off a future situation where Egwene gains control. Any such move by her would have required a minimum of 14 Sitters to be present (that's the quorum in a 21 Sitter Hall), and however Egwene played it, there was no way she could play it so that no Rebel was one of those 14, since 10 of the current Sitters were Rebels. One or the other of those 14 could simply have given warning about the Law of War.

And, as Egwene pointed out, there wasn't any realistic way they could stop her. A proclamation making the Hall in charge of the War would require the Amyrlin's assent, so this meeting couldn't have been about that.

I think the meeting was supposed to be of those who felt Egwene had too much power already/were disgruntled with her decisions post-reunification for one reason or another. The Law of War was being discussed as the Rebels wanted to make it clear Egwene wasn't a political lightweight. The plan was probably to limit her power in some other way.

Where this fails is in the presence of Ferane and all the Green Sitters. Ferane, at least, shouldn't want to limit Egwene, since she was all but giddy that they were setting up an Amyrlin of strength in tGS. Same with Adelorna, which makes the strong presence of the Greens a bit of a mystery.