I think part of your problem with this is that you're looking at it from the logical fallacy of the end result. If you look at the chain of events from the beginning, it is so highly unlikely that Rand would have found out about this situation to lead him to Graendal's manor. In fact, he didn't, if he didn't have Nynaeve with him, it would have all gone undiscovered in the first place. Sure, it's a series of extraordinary events, mixed in with some, in retrospect, ridiculous moves by a Forsaken.
Really, is it any stupider than Sammael moving the battle from a place he knows well to a haunted city with an unstoppable monster residing in it that would like nothing more than to destroy him? I don't really think so.

The thing of it is, while it looks to some silly that Graendal did the things she did, they worked all this time, and she was fine. It only looks foolish because in the end it spectacularly backfired on her.