There is also some symbolism in her journey down the road from her high class house on the hill down to the lower class cottages at the bottom of the hill. The fact she lowers herself to visit and pay her respects is symbolic. The story also uses a lot of light and dark imagery for symbolic purpose to illustrate the differences in the classes. The array of white flowers and the arum lillies, and banners, and creme in the creme puffs is in contrast to the dirty, dingy homes of the poor. Even the smoke coming from their chimney's is described differently. The poor cottages have smokey smoke that blocks the light, but Laura's house's smoke is described as a silver plume. The colors of clothing are symbolic, as are the contents of the food basket, the garden (of Eden) vs. the real world of poverty and death, Josie's song, and just about everything else in the story!
The most developed symbolic element in the story is the hat. Look at how often it is mentioned, and how it seems to carry an emotional charge. When Laura reacts with guilt (and near shame) at wearing the hat to the funeral, this shows she is growing, and that she isn't quite the same as the rest of her family, who are bound by their class.
I'd say that her lines that don't get finished are also symbolic. She doesn't quite know how to finish her sentences—or be herself—in the context in which she lives.