... you are claiming that Graendal left Kerb behind only to lure Rand to Natrin's Barrow, which requires of course that Graendal knew enough about Rand and his entourage to know that he would have a conversation with someone knowledgeable in herblore that would drive that person to find a clue to Graendal's whereabouts to prove her self worth, within the approximately one week timeframe between which the poisoning had begun and could be noticed by a sufficiently astute Wisdom but before she died, wiping out all traces of the incident. It also requires that she would then know that Rand would wipe out her entire palace from a distance rather than attempt to face her directly, so she could escape.

And all this for what, exactly? So that Rand would think she's dead? What does that bring her, exactly? Your convoluted plan assumes that the only reason Rand found Graendal in the first place was because Graendal planted a lead, so if she didn't want to risk Rand coming after her, she should simply not have planted that lead at all! And if she's still scared, then she could simply Travel, anywhere in the world, and Rand would never be able to find her.

So we have this huge, ridiculously convoluted plan which requires months of forethought and quasi omniscience in order to achieve essentially nothing.

This doesn't make Graendal look brilliant. It makes her look like Wile E. Coyote. If he can order rockets to go after the Road Runner, why doesn't he just order some chicken?