The woman was immediately shaken.
She felt like the first thing she should have done was refute Ryu's claims as ridiculous. But, the moment she heard them she realized that it was the only possible truth. All of her previous conjectures seemed worthless.
Like Ryu said, she initially thought that there was truly an assassin. Unlike Ryu, she couldn't just 'see' what was happening. She had to use her Sword Dao to comprehend the battle scars. The more she comprehended, the easier it was for her to 'see' what was happening. But, even then, it felt a lot like going in blind.
Simply put, Ryu was watching a movie reel while she was reading some obscure ancient text written in a long lost language. Not only did she need to translate and decode it, but there were many blanks she had to fill in herself.