Oh, since I've mentioned demiurges without clear agenda in case of their victory in K6BD, I kiiiinda don't really follow the issues Jadis has?
Here's her profile shot from the comic; the hole in the background is the aperture of the machine.
See, ten generations of her ancestors built a vast machine for prognostication. In the end, when it was turned on, giving them perfect omniscience, her relatives were killed, and she was locked permanently in a block of ice. That doesn't really deter her (she teleports across the worlds as needed, and appears as a projection whenever she feels like that). What does is the omniscience - in her own world, the past, the present and the future are inscribed in a piece of amber, vast and unchanging. Thus, to her, there is no purpose to any action at all, since she knows in advance both the actions and their consequences (and in the mechanist, predetermined universe of K6BD perfect predictive omniscience is possible).
And, uh, I struggle with this setup on two issues (well, not only me, of course, Jardiscourse was very common in the fan spaces during her arc).
First is the pointlessness of any action when knowing its end results. Consider that we will all die. Except for a handful of us, a century later no trace of our existence will remain. For the rest, the consequences of their actions might last a little bit longer, but even then, in but a blink on the cosmic scale, they will be gone and forgotten. But that is not stopping us from taking whatever actions we consider proper in whatever time we still have alive, is it?
Second is the omniscience itself, and the paralysis that comes with it. We've seen that she does take some actions - simply as evidenced by the fact that she pulled Allison from Rayuba, and took care of her afterwards.
And however Jadis' omniscience works, I can't quite understand why it should interfere in her decision-making process. Whether she gained a perfect snapshot of the multiverse, which allowed her to predict future and reverse-engineer the past perfectly, or whether she gains continued insight into each and every object of her attention, with perfect predictions of consequences of any given action. I can only see two possible outcomes for possessing such an ability, let's call them omniscience-perfect and omniscience-agnostic.
Omniscience-perfect is Jadis making every decision she ever has to make based on perfect predictive information; that is, always choosing the strictly optimal action. Of course, that shouldn't universally lead to victorious outcomes (she has omniscience, not omnipotence), but there's no reason for her to ever say wrong things when interacting with people, for instance, or to miss her targets with spellcasting. The omniscience-perfect outcome obviously cannot be constant inaction and decision paralysis, because of course inaction is not universally the optimal course of action (although of course sometimes it is).
Omniscience-agnostic is Jadis learning of the decisions she will make aaaaall the way to the future, until her death, the moment the machine is turned on, with the decisions made as if she didn't possess the omniscience, and still frozen in time as inevitable. Then I cannot see what the omniscience changes at all, other than perhaps Jadis' own interiority state, since she's still bound to take the same actions the would've taken without the omniscience to begin with.
In both cases, of course, for an outside observer the decisions Jadis makes are, generally speaking, indistinguishable from not possessing omniscience. The reasons are obvious from the omniscience-agnostic scenario, but even for omniscience-perfect, the perfect decisions made can appear erroneous or random because the observer does not possess the omniscience to factor all the circumstances needed for making them perfect.
And that leads us to the final conundrum about the character - how much of what she says to Allison is true at all? She's shown as a victim of her abusive family that thrusts upon her a curse of universal knowledge that she did not want, which ruins all of her plans for being a benevolent ruler of her worlds, as she's now paralysed by that knowledge. But how much of this is true, given how little sense it makes in any omniscience scenario? And how much is simply manipulating Allison for when she wins (which Jadis of course knows if she does)? After all, using OOC knowledge, Jadis the White Witch in Narnia was a liar.
