Well, there's some reason to think this isn't really a duplicatible event. This story is all about avatars trying to reverse their relationships with their sources. Rama Khan is the servant and guardian of Jarhanpur, but tries to behave as its master and dictate it on his terms, and Jarhanpur revolts and falls down around him. Diana is the servant and guardian of the Truth, but tries to behave as its master and dictate it on her terms, and the Truth revolts and falls down around her. But this is not something that Diana is ordinarily capable of doing - she's not so perfect that she's never denied the whole truth before this, or hasn't since, and yet this is the only time reality has dissolved. Only in Jarhanpur, where the magic is strong and the walls of reality a little thinner, was she able to exert enough command over the Truth for the Truth to have to fight back. The lariat, powerful focus though it is, would need someone much more powerful than Diana to be able to do that kind of thing again all by itself, and Genny's command of despair/hatred/whatever doesn't seem to significantly outstrip Diana's of Truth in that sense.