After the death of her ally Rue, Katniss covers the body of the young girl with flowers as a symbol of Rue's humanity and a tribute to her short life. By calling attention to the sacrifice that Rue made during the Hunger Games, Katniss challenges the idea that Hunger Games – and the people who play them – are mere entertainment for the audiences back in the Capitol. For Katniss, Rue isn't simply a character on a television show. She is a human being who is worthy of respect, admiration, and mourning.
As Katniss says:
"I want to do something, right here, right now, to shame them, to make them accountable, to show the Capitol that whatever they do or force us to do that there is a part of every tribute they can't own. That Rue was more than a piece in their Games. And so am I." (18.38)
Covering Rue with flowers is an intense act of rebellion against the Capitol. The experience of witnessing Rue's death inspires Katniss to go on and win the Games – and to prove to the Capitol that they can't strip the tributes of their humanity, however they might try.