Shiori was so blind as to believe that Shuuichi was what he said he was. After all, she was a minor spirit-user. She was trusting; not oblivious.
As her son walked into the room, she smiled kindly. It was the least she could do. After all, he was the reason she lived. After her psychic husband's mishap with the demons, he was the only reason she didn't commit suicide.
Of course, she knew he was hiding something from her. How could he not be?
Even though she wasn't a very good spirit-user, she could see the strange aura surrounding him.
There were his friends.
She had heard of the notorious demon bandit, Hiei, from her husband. The price on the head of this powerful demon was so large that even her husband was sucked into the rage of killing him and collecting the reward.
When Shuuichi walked through the front door with an injured Hiei slung over his shoulder was when she realized her suspicions had been correct. She knew there was something demonic about him, and seeing her ten-year-old son walking into the house with Hiei really set her mind off.
Then there was Genkai. He never really mentioned her, but Yusuke once said to her to relay a message to him about meeting at Genkai's temple. Shiori wasn't so ignorant not to know of Master Genkai.
Yusuke was another strange one. At first his aura was completely human, and he would send of major power auras, but lately it's been raw youki, which led her to believe he had demonic heritage.
Along with Yusuke there was always Kuwabara, who would make his aura stronger as he spoke. She wasn't sure if it was intentional or not, but it was a useless scare tactic against street punks and spiritual unaware humans.
She once met Yukina too. An obvious demon if she ever saw one. A koorime. Her innocent, naive personality gave that away.
Yusuke and Kuwabara always slipped-up too. Calling him the wrong name. Sometimes they would catch themselves, sometimes they wouldn't, but it had been explained as a nickname.
But Shiori was not oblivious. She had heard of Youko Kurama and his banc of thieves. She had heard of how he was impossible to capture, and she had heard of his death, and even more, his rebirth.
Shiori wasn't so blind as to not know Shuuichi Minamino wasn't truly Shuuichi Minamino.
Her son was Youko Kurama, and that, she was sure of.