RJ/BS just wanted to show Graendal at one point and remind the readers where she is, what she does etc., before she is killed later. The prologue seems like a perfect place for this.

Likely Granedal even did a bit plotting in the meantime, e.g. influencing some members of the Council of Merchants, getting reports from her spies and rallying DF. IIRC, there also wasn't that much time between Moridin's order in the prologue and Graendal's death, so that it's not implausible that she just started to get her plans concerning Rand in motion and stayed in Arad Doman till then.




IMO, BS just didn't want to give a "Graendal is toast"-confirmation yet, because we shall discuss it a bit more. But ToM will make clear that Graendal must be dead and after this book BS will give us a definite "Graendal is toast"-quote (similar to the situation of Sammael's death).




But apparently their shoes were balefired, too.

In Graendal's case it's said that "a column of pure whiteness exploded from him [Rand] and burned across the silent night sky, illuminating the trees below it in a wave. It moved as quick as a snap of the fingers, striking the wall of the distant fortress. The stones came alight, as if they were breathing in the force of the energy. The entire fortress glowed, transforming into living light, an amazing, spectacular palace of unadulterated energy. It was beautiful. And then it was gone."

So, initially only one wall is hit by the balefire column, but then the whole palace vanishes (which doesn't necessarily mean though, that there might not lie Graendal's small angreal somewhere on the field and Rand was just too distant to notice).