Diana Duncan 
Sam the Scaredy Cat Dog [EPUB ebook] 

Although Sam, Cleos dog, is enormous, he is a real wimp. Cleos mum urges him to be brave because he is frightened of everything; even Punky the poodle from down the road and Fat Felix, the cat who hangs around the park.
But one day when some bullies decide to pick on Cleo as she skips off to school, Sam suddenly finds the courage to defend her and also lands himself a splendid daytime job!