 Cooper returned to Leipzig and documented her experiences living in wartime Germany from 31 July 1914 and 1 December 1918 in 227 weekly letters to her sister.It was not possible to post the letters back to Australia, so the first 52 were smuggled to Switzerland.The rest of the letters were hidden in music scores and furniture until she could send them from England in 1918.

Cooper's sister, Emmie, later deposited the letters in the State Library of South Australia's collection.