Do we know how much time passed between Graendal's PoV in the prologue and her death? Because it's quite possible that Graendal was indeed still plotting how to break Rand (not an easy deed), since Rand just came to Arad Doman. It make sense that she would first try to get spies close to Rand to study him, since we learned in the beginning of TGS that she only knows Rand from pictures (which makes it quite difficult to predict how Rand will act).

Furthermore, I doubt that the DO, as the "ur-control freak", would agree to a plan, where he gives his archenemy, the Dragon, access to his True Power.

Besides that, we learned in the series that the Forsaken aren't that clever. Therefore I'm certain that those theories that Graendal's "death" was just a big ruse and actually everything goes exactly according to Graendal's brilliant masterplan will prove to be wrong the ToM.

It doesn't make much sense that RJ would trick us with Graendal's death so late in the series, if it's just easier to let Rand kill her for good and concentrate on other things. After all, what would be the point? To show that the hero of the series, Rand, actually couldn't outsmart Graendal, because Graendal is truly the most clever character around and easily outsmarted Rand. Therefore Rand or someone else has to come up yet with an even cleverer plan to kill Graendal in her new lair, wherever it is.

This doesn't fit at all with RJ's perception of the Forsaken as flawed people (Semirhage can be broken, Graendal can be outsmarted), would be a completely redundant twist and just reduce the significance of Rand's act to kill Graendal.

The events happened too quickly and partly by chance, namely that Nynaeve found Graendal's Compulsed spy in time, that she was then able to remove the Compulsion on the youth, that Rand could actually still force him to tell the location of Graendal's lair before his death, and that Rand then invented his unorthodox method to kill Graendal and be sure of her death.

Graendal simply couldn't predict all this.