I have been researching the Campbell side of the family the past couple of years. This is what I know about the census record that you have:
Hugh Gaddie m. Lucinda Louella Campbell. She went by the name of Ella. They had a child named Arimnda Belle Gaddie b. in 1900 (I guess after the census was taken). Others listed are Belle Gaddie (Leanna Isabelle Campbell, Ella's sister), Ella and Belle's mother (Delitha Jane Cooper Campbell).
So...Belle Campbell is not Hugh's sister or his mother but Ella's. I hope this helps. Do you know anything about Arminda Belle Gaddie? She would be the niece to my great great grandfather. I have been searching for her for some time now.