Probably the easiest way to think of it is as a two-way tunnel between her sword and a position she has to set up beforehand. Since she has to touch the blade against wherever she's setting the end-point of the 'tunnel' its much less useful if she doesn't have any time to set up. In a long, drawn-out fight, she might be able to set something up during the battle, but that would depend on how much her opponent is pinning her down and putting pressure on her.