Yin Yuan was someone who did not underestimate her opponents and would look into them. She had prepared quite a bit after learning that she was fighting Lin Mu who had defeated his previous opponent in record time.
She was wary of Lin Mu's powerful attack and knew that it could happen with her too. Thus, she prepared a defensive high grade Immortal tool that would be able to protect against it immediately if she didn't react in time.
But much to her shock, the barrier didn't last and yielded against the very first attack. Not just that, but it seemed to be different than the one Lin Mu had used in his previous fight.
The subsequent attack of Lin Mu also caught her off guard and if not for the fact that it was weaker, the Hexapole Repulsion Pill technique might not have been able to slow it down.