Si Kongchen was watchful. He couldn't sense Lin Qiao when there was a distance between her and himself, but once she came closer, he would definitely detect her. Therefore, it might not be easy for her to directly bring him into her space and kill him.
She had to find a way to distract or agitate him.
Lin Qiao watched Si Kongchen finish the cigarette and then head back toward his office. She followed behind him, keeping a distance from him. She didn't follow him all the way into the office, because the office was only about a hundred square meters. He might detect her if she went in.
She couldn't release her power into the office either, as all level-eight beings were highly sensitive to superpower energies and vibes and could detect even a slight amount of energy. That was why Si Kongchen was able to sense Lin Qiao's presence when the latter was invisible.