The strike wouldn't fall upon her as hard as it could have, perhaps due to her sword, perhaps simply due to her sheer stubbornness.  However, Zhou wasn't going to take it easy on her.  Each swing of his sword sent more lightning at her, an attempt to overwhelm her with the sheer amount of blows he could rain down upon her.  His temper was rising, and his desire to hold back was quickly falling to the wayside.