The Rose Code by Kate Quinn

The third book by Ms. Quinn set in or around World War II.  This one involves three heroines from different backgrounds working at Bletchley Park, the famous location of codebreaking in England during the war.  Mab is a girl from Southwitch who lives with her mother and sister (actually her daughter).  Osla is a welathy debutante who falls in love with Prince Phillip (before Elizabeth).  Beth is a shy, downtrodden, genius with math.  The three of them end-up in the same home while working at Bletchly park as code breakers.