Can you relate the flashbacks in this book to mood and overall plot?

Sepetys uses flashbacks to expose Lina's past, all while keeping the plot of the story moving forward. These flashbacks serve to reveal her personality and help the reader understand her. The flashbacks to Lina's childhood give us a bittersweet glimpse of her childhood.... the time before her her family was taken by the Soviets. They also serve to alleviate the mood of heartache and devastation..... if only for awhile.