Rue is the tiny, twelve-year-old tribute from District 11, the agricultural district. She can fly from tree to tree and is a wonder with mockingjay bird calls. Despite her size, she scores a surprisingly high "7" during her training sessions (8.34). Her name, also, means "regret" or "sorrow" (source), which is a bit of foreshadowing as to what her fate will be in the Hunger Games.
Rue reminds Katniss very much of her sister, Prim. Katniss acts as the primary protector of Rue once the two become allies. In this sense, she continues the role that she formerly played with her sister, Prim. Katniss and Rue share food, supplies, and stories about their lives. Katniss learns that Rue is the oldest child in her family and she loves music. Rue becomes human to Katniss and not simply a competitor. Their brief friendship during the Games allows us to see Katniss as a nurturing character, even in the midst of all the fierce competition.
After Rue's death, Katniss honors Rue's body by covering her with flowers (Chapter 18). (See our section on "Symbolism, Imagery, Allegory: Rue's Flowers.") This act is that defies the Capitol and challenges the idea that Rue's death was just entertainment for a viewing audience at home. Rue was human and she made a great sacrifice in giving her life during the Games. Ultimately, Rue's death inspires Katniss to fight all the more against the Capitol – and win the Games any way she can.