Leona demonstrates what individuals can do when they feel empowered. The citizens of Gibb Street feel they can't do anything to change their surroundings, but Leona's actions show them that they could make a change for themselves.
Leona is a great example of a idealistic realist. She knows what she wants (to clean up the Gibb Street lot), but she also knows what she has to do to get it (sit on the phone all day). This is best shown when she chooses to bring a bag of trash right to the office waiting room: She has found a realistic way to make her ideals known.