This is wonderful. I love stories that humanise the Dursleys, and Petunia in particular*. The photographs were a wonderful way to catalyse that, and the memory of Lily in the garden was just beautiful. I love the contrast between Petunia, who has learned from and accepted (at least, the way I interpret the story) the past, and Snape, who doesn't seem to have learned much at all.

*You even humanised Vernon a little, though, and that takes some seriously good writing. :)