When Nancy spends her first night at the home in Hollywood, there is a digital clock/radio on her bedroom nightstand. In the next scene, it has been replaced by a old-fashioned wind-up alarm clock, which awakens her. Nancy mentioned she likes old-fashioned things. It is possible she took the alarm-clock which had been there and replaced it with her own.
Nancy loads a VHS tape of "Twilight in China" into the VCR to look for the clue in Dehlia Draycott's movie. The tape is rewound to the beginning when she loads it - yet it immediately jumps to the "Make the dragon bow" scene; which, according to Dehlia's lines, is most likely in the middle or at the end of the movie and nowhere near the beginning. Even if it's a prologue, Nancy still should've had to fast forward through the previews that came before the movie.
During the chase scene between Nancy Drew's Nash convertible "roadster" and the bad guys' Range Rover (starting at 1:20:20 on DVD), the Range Rover bumps the Nash three times. Nancy Drew's head snaps forward when physics would dictate that her head would first snap backwards (i.e. whiplash).