What is the main conflict in Shooting the Moon by Frances O'Roark Dowell?

Shooting the Moon is a novel by Edgar Award-winning author Frances O'Roark Dowell. The story follows the main character, Jamie Dexter, as she transitions from a 12-year-old girl to a teenager while her older brother enlists in the Army and heads off to Vietnam. When Jamie is moping around the house over the summer because her two best friends have moved away with their families, she gets a job at rec center on post. While working at the rec center, she mingles with GIs that have been to Vietnam, or who are waiting to go. She befriends Private Hollister, one of the soldiers assigned to run the rec center. The 19-year-old soldier and the 12-year-old girl strike up a friendship that includes a summer-long championship game of gin rummy.