The Secret Stealers by Jane Healey

Another book about the contributions of women in World War II.  In this one, an American widow with connections goes to work for the forerunner of the OSS.  At first, simply as a secretary to the General who is running the operation, then as a spy.  She is trained in how to operate and encode messaging equipment and sent to France to help the underground, where she is reunited with childhood friends.  Since she is fluent in both French and German, she works as a waitress in restaurant where she can overhear SS officers.  This is much like the heroine in The Alice Network.