Visible crew/equipment: When Nica is pushed through the railing by Chucky, you get a quick but clear look at the stunt double's face, who looks nothing like actress Fiona Dourif. Her arms noticeably also get more toned when this happens. Finally, for a second, you can see her moving her one leg, which shouldn't happen since Nica is supposed to be paralyzed.
Visible crew/equipment: When Chucky kicks over the bucket to electrocute Jill, you can just barely see something small and white sticking out from underneath the bucket, which moves when the bucket tips over. It appears to be part of the mechanism that actually "kicks" it over.
Visible crew/equipment: When Nica rounds the corner to answer the door in the opening scene, as she gets close to the door, you can see the shadow of the cameraman on her back for a moment. (It's right after she says "Well, I'm used to that.") You can also VERY faintly see it on the door a few seconds later.
Answer: The films don't delve into either Chucky or Tiffany's backstory, and the films themselves are the only official canon. So until it is properly addressed in the movies, it's basically up to your imagination.