But wasn't she controlling it already with the specially keyed lightning glyphs? Locking the entrance down even as she still has the various flavours of guards rounding up the citizens for enchanting would be strange and speak of her suddenly getting afraid of Soriel to the point of hunkering down even though her thing at that point is assuming her superiority - unless it's done with another of the anti higher demon glyphs which just blocks the entrance by default without her needing to even look (incidentally that could be an explanation for why Nefris never joins the party in liberating the ziggurat). But then that would tip him off to the fact that those glyphs are a thing, and the first glyph encounter has to be a surprise to set off the prison sequence.
Well, I'm curious to see where it goes.