I found this odd when reading the book. Why did Reiko not pass on information about Naoko's condition to Watanabe till its too late?

[Andrea]

After reading a comment here about Reiko possibly not really being mentally stable, it occured to me that the manipulative, sick girl Reiko describes to Toru could very well be herself. During Toru's first visit, she seems to lead Toru away from Naoko and starts discussing her story with him. Then she tells Toru to let Naoko sort her problems by herself. In the letter she writes to Toru after Naoko's suicide, Reiko tells him that Naoko's condition kept getting worse after his first visit to Ami San. Why did she not tell him this before? I, like Toru, believed Naoko was getting well. And then Naoko suddenly commits suicide. Also, what Reiko said to Toru about Naoko's death made me a bit suspicious. "So then the ambulance came and took Naoko away and the police started questioning me. Not that there was much doubt. There was a kind of suicide note, and it had obviously been a suicide, and they took it for granted that suicide was just one of those things that mental patients did ('did' is italicized for emphasis in the book)."