How was Katniss's decorating Rue's body a noble act in The Hunger Games by Suzanne Collins?

Let's try to define what a noble act is first.  A noble act is a chivalrous act.  It is an act or action in which the welfare of another person is put before the person doing the act.  The act might involve courage, but it doesn't always have to.  For example, giving up your seat on a bus for an elderly person isn't brave, but it is noble.  You are treating the person with respect and dignity.  It might even be at your own expense, because the act might cost you time, energy, or money.

Thinking of Katniss's decoration of Rue's body as a noble act is interesting because Rue is no longer alive.  She cannot benefit from Katniss's action.  Nonetheless, Katniss's action is noble, because she is treating Rue (her body) with respect and dignity at the possible expense of her own safety.  Katniss is leaving herself vulnerable to attack and/ or wasting precious time that could be spent gathering supplies to help herself stay alive.  Katniss's act is noble because she doesn't gain anything (immediately, anyway) from it, nor does she expect to gain anything from it.