I guess she is a bit suspicious... But then she's pretty hyper for a oba-san . And she isn't the smartest person...
Other than that, basically what User 4869 said. She also knows Conan is Conan. Besides, if Shinichi's log was in the 'People who had taken the APTX4869 book', she would act against it somehow, right? She is his mother...
Also, wouldn't Yusaku have figured out her secret identity?