Her demise was sort of fine too me. Graendal solidly misinterpreting the most "simple" foe she's had to deal with (Perrin and his straightforward thinking that surprises the convoluted minds) and ending up SH's pet is the very type of ironic demises RJ liked so much.

Brandon didn't quite "get" Graendal indeed, though. Her depiction was fairly disappointing (she lost a bunch of IQ points, like many other characters such as Lelaine) and left much to be desired (including contradictions, like having her leave a window open and enjoying the view and fresh air. Previously we had been told she disliked seing the outdoors so much she used only the inner rooms without windows in her palace.

But I mostly disliked how Brandon split her confrontation with Rand between the two books instead of putting her reaction scenes in TGS where they belonged, with an unecessary and boring fake cliffhanger instead. I remain pretty convinced in RJ's mind Graendal was to escape Rand only to end up found and punished by SH, and that (as is typical of RJ's plotting style), the Forsaken ordered to use Slayer and the dreamspike against Perrin was not her and never actually seen on-screen or identified (and was probably Cyndane or Moghedien, if Moridin had not simply given his orders directly to Slayer). A remnant of that seems to appear in TOM, when we're told Cyndane and Moghedien were busy in the south trying to obey the orders to kill Perrin/Mat, only to see Moridin give the job to Graendal all of a sudden, for no obvious reason beside making it possible to put the aftermath of her confrontation with Rand in TOM. Anyway, my gripe is only that the Rand-Graendal confrontation (and what leads up to it) was really nowhere as good as it could have been because of the split of the scenes, and it destroyed the red herring RJ had prepared in KOD with Aran'gar planning to disappoint Moridin about leaving Rand alive, and to use Graendal's networks in a way Graendal wouldn't disapprove of. The scenes should really have been kept in order: Aran'gar squats at Graendal, Graendal is given delicate mission about Rand and we know Aran'gar has other plans and might totally make Graendal's mission go completely wrong (making us wonder through TGS if Rand is facing Graendal's schemes or Aran'gar's interferences, and knowing Rand was planning for Graendal's style of games but doesn't know he might be facing a Balthamel-style plot instead). Then the resolution: Graendal escapes by framing Aran'gar only to end up punished as SH's pet. That's how rather obviously RJ planned it. Brandon kind of ruined and dumbed down that storyline the way he split the books.