«Lily's Dream» by Judi Curtin

The further adventures of Lily: life as a maid in Lissadell House is always interesting, but with her friendship with Maeve under strain, a war in Europe starting and uncertainly about her future, she needs all her wits about her! This latest installment in the popular series also sees Lily finally on her way to realising her dream of becoming a teacher.
Nellie's older sister, Johanna, starts walking out with Harry the footman, and is extremely worried when he enlists and goes off to fight in World War I. He send letters to the girls from the front and tells them all about the Christmas Day truce in 1914 … but then a telegram comes. Harry is missing, presumed dead.  Will he return to Lissadell, safe and sound?
Meanwhile, when Isabelle, the children's nurse, becomes unwell Lady Mary asks Lily to work with the Michael and Hugh Gore Booth in the afternoons until they are ready to go away to boarding school. On a visit home, Lily meets the Master, who tells her that Miss O'Brien is courting a young man — and if she marries, there will be an opening for a Junior Assistant Mistress in the school. He assures her that her current level of education will be enough, and that once she is old enough, he'd be happy to appoint her.