"Brownies" is a short story by ZZ Packer, part of her 2003 anthology Drinking Coffee Elsewhere.
In the story, a group of Brownie Girl Scouts plans revenge on a rival troop for a perceived racial slur. They hike to the public restroom to lie in wait, only to find it very messy; when their nerve fails and they leave, one girl, Daphne, remains behind, cleaning:
...she began again, picking up leaves, wads of paper, the cotton fluff innards from a torn stuffed toy. She did it so methodically, so exquisitely, so humbly, she must have been trained. I thought of the dresses she wore, faded and old, yet so pressed and clean. I then saw the poverty in them; I could imagine her mother, cleaning the houses of others, returning home, weary.
(Packer, "Brownies," Google Books)
Since Daphne is poor, she is introverted, and is in this case being used as a stalking horse; the other girls have laid the "hearing" of the racial slur on her. Daphne tags along because she wants to be accepted, and she starts to clean the restroom because she is uncomfortable with their prejudice and anger; she reverts to the lessons of her home, where cleanliness is a virtue. It is hard to be poor, but many poor people take pride in their cleanliness, because they don't have to be poor and dirty as well. Where the other girls leave the mess because they don't care, Daphne sees that the dirty restroom as something intolerable; she is not concerned with their planned revenge, but she can do something about the mess.