When Cody's dad returns from the mainland with a young girl, the bots and Cody find out that she is his sister, nobody knew that Cody had another sister Chief's wife didn't want him to find out so shortly after Emily was born they found out that she had disabilities, so Emily's mother decided to give her to a mainland facility that could take better care of her, that was eight years ago but now Chief makes a trip to the mainland to go and visit his daughter. This is set shortly after season 4 ends.