Laura is a young lady on the cusp of womanhood, but she is still treated like a child by her family, albeit in a generally good-natured way. Although her mother has told Laura and her sisters that she has left the birthday party arrangements to them, she is the one who takes charge of everything. Laura herself tries to get involved, but she is pointedly not permitted to decide where in the garden to locate the large tent where people will celebrate her birthday.
All this would appear to suggest that Laura's birthday party is as much an opportunity for her family to show off as it is to celebrate her life. More than anything else, this is an important social gathering, and Laura's mother is keen to make sure that everything goes off without a hitch. It would probably be an exaggeration to say that Laura is being taken advantage of here, but her mother sees her birthday party as so much more than just a party and is undoubtedly the guiding spirit behind the events. This party will be as much a celebration of Mrs. Sheridan as it will be of her daughter's birthday.
When Laura suggests cancelling the party out of respect to the deceased Mr. Scott, it is telling that Mrs. Sheridan dismisses her daughter's suggestion out of hand. Mrs. Sheridan is so incredibly shallow that she simply cannot bear the thought of being deprived of an opportunity to dazzle and impress, especially because of the death of a lower-class neighbor she hardly even knew. Mrs. Sheridan then proceeds to manipulate Laura's emotions by getting her to see just how pretty she will look to all the guests in her beautiful hat. In this particular instance, one can say that Laura is being taken advantage of by her mother.