One of the many potential themes that you could comment on in response to this question is that of class. Essentially, this is a story of a young woman who is made to realise the importance of class in spite of her desire to live her life as if it was not important. You might wish to consider how the character of Laura and her impressions are presented. Consider the following quote:
And now there came the chock-chock of wooden hammers. Some one whistled, someone sang out, "Are you all right there, matey?" "Matey!" The friendliness of it, the--the--
This quote shows how Laura looks favourably on the working class men as they ready the garden for the party. Imagery is of course best when it combines as many of the senses as possible, and here we have the sense of hearing combined with Laura's sight of these working class men. Imagery is used deliberately to present them as being pleasant and positive, which helps highlight the theme of class in this story.
Of course, in spite of this, you might want to go on to explore the way in which the story presents Laura as being unable to escape from class conventions, no matter how much she may like to. Hope this helps!