Billa of Ingleside by LM Montgomery

Anne Shirley's children are almost all grown up - except for pretty, high-spirited Rilla, who is almost fifteen years old. Rilla's thoughts are filled with going to her first dance at the Four Winds lighthouse - and getting her very first kiss from handsome Kenneth Ford.
 
But at the dance, news is announced that England has declared war on Germany. At first, this means little to Rilla, on the threashold of so many new excitments. But as her brothers go off to fight in the Great War and Rilla brings home an orphaned newborn baby in a soup tureen, she is swept into a drama that tests her courage and will leave her changed for ever...