Why do newspaper put "Frankie" instead of Frankie when it is the name of an animal? ie "Susan M and her dog "Frankie" witnessed the burglary but could not give a description of the burglar".
Because their style guide says so ! The convention is to put nicknames in inverted commas thus: Ian 'Beefy' Botham. The paper has extended this to the cat's pet name. That's only logical if the cat has another, formal, name such as Everdale Franklin's Queen at Borrowdale and is known at home as 'Frankie',