In "A Photograph," the poet's mother laughed at the snapshot. What did her laugh indicate?

In "The Photograph", the speaker's mother laughs at the image of herself as an adolescent holding hands with her younger cousins on a beach. The speaker's mother laughs with nostalgia as she remembers the time she spent on the beach.
The laugh of nostalgia may also be rooted in the speaker's mother thinking about her childhood in general and the ways in which time changes us and often takes away the innocence we held as children. Photos such as the one described in the poem can evoke so much emotion and reflection about mortality and the passing of time. As the speaker's mother gazes at the photograph, her laugh may also indicate a reflection on lighter and less serious times.