The best way for Graendal to convince Rand that she is not there is send the man away without Compulsion. She sent him away covered in weaves. It was like a giant sign in the sky and not her plan at all. There's no way she could have known that Rand was right outside her palace waiting. If she'd set her weaves to unravel, the lord's sudden change in personality would have baited Rand even more. None of it makes any logical sense.