If we are going to be consistent with characters, Graendal is a character that can't be beaten by violence because she uses her mind as her weapon, thus it makes sense that when he results to using brute force, she isn't there to be caught.

The difference is that Graendal did not attack him directly, unlike the other Forsaken, so he did not have the opportunity to pinpoint where she was, and since he didn't kill her face to face like the other Forsaken he hunted down, it is possible his blow didn't land on her.

Rand used a punch as an example, but Graendal may be an enemy you need to defeat by either playing chess or some other game. IE: She may not have been at the table he thought she was sitting at when he launched his punch. Somewhat like the US military firing rockets in strategic locations where Bin Laden can be, but not being sure if they actually got him or not due to how he operates.