Actually, it's easily been struck down: it's ridiculously unlikely and ridiculously futile. There is no way she could have done it and no reason for her to do it. Therefore, the coherent solution is that she didn't do it.

She couldn't have done it because it requires a number of highly unlikely incidents that were likely influenced by Rand's ta'veren presence. Only a channeler would have been able to Delve Milisair. Only someone with knowledge of herbs could have identified the poison. This person would have to find and Delve Milisair within the one week time window between the beginning of the poisoning and her death - and the poisononing had to be begun before the investigation, so that time window had to be very well predicted. Which, as we know, means that Graendal had to predict the conversation between Rand and Nynaeve, and Nynaeve's reaction to it. Then she had to predict that someone would be able to unravel her Compulsion, something that is generally considered impossible. And that's to say nothing of the Compulsion on Ramshalan. Then she had to predict that Rand would balefire or otherwise wipe out Graendal's entire palace from a distance, something that is completely different from his modus operandi in dealing with Forsaken thus far: he confronted Aginor, Be'lal, Ishamael, Lanfear, Rahvin, Sammael and Semirhage in person, after all.

And your argument is that it is a plot hole that Granedal did not predict all this? The position could hardly be more ludicrous.

And there is no reason for her to do it because it achieves nothing. For an argument that revolves around 'Graendal wanted all this to happen!', you seem to have omitted to explain why she wanted this to happen.