School for Skylarks — Sam Angus

It is 1939. When Lyla is evacuated from her home in London to her great-aunt's enormous house in the West Country, she expects to be lonely. She has never been to school nor had any friends, and her parents have been at the centre of a scandal. But with the house being used to accommodate an entire school of evacuated schoolgirls, there's no time to think about her old life. Soon there is a horse in a first-floor bedroom and a ferret in Lyla's sock drawer, hordes of schoolgirls have overrun the house, and Lyla finds out that friends come in all shapes and sizes.