Portrait of Faith Hinckley in her formal "Y" girl uniform.

P. Faith Peters flips through a scrapbook compiled by her grandmother Faith Hinckley, a "Y" girl, during nine months of service in Europe.

P. Faith Peters flips through a scrapbook compiled by her grandmother Faith Hinckley, a "Y" girl, during nine months of service in Europe. The right-hand page contains Hinckley's "honorable discharge" document.

A scrapbook compiled by Faith Hinckley, a "Y" girl, during her nine months of service in Europe.

The engraved backside of a watch given as a parting gift from the 56th Infantry to Faith Hinckley, a "Y" girl who served in France for nine months.

From left, a "cootie bracelet" worn by Hinckley in France; the engraved backside of a watch she got as a gift from the 56th Infantry; and a pair of medallions given to her by a soldier after she served nine months in Europe.

"Forgotten Fires," a World War I memoir written by "Y" girl Faith Hinckley and published in 1923.

A pair of medallions given to Faith Hinckley, a "Y" girl, from a U.S. Army soldier as a parting gift after Hinckley served nine months in Europe.

P. Faith Peters, in her Portland home, holds a portrait of her grandmother Faith Hinckley, who was a "Y" girl for nine months in France. At right, a portrait of Faith Hinckley in her formal "Y" girl uniform. An exhibit featuring Hinckley's service in World War I goes on display July 14 at the L.C. Bates Museum.