Chapter 24: On the way to the lake, Katniss recalls Glimmer's body and Rue. Why might Collins have included these details just before the final battle?

I think Collins wants to show us Katniss's character at this point in the book. Although she and Peeta are still alive, Katniss has not forgotten who has been lost. She has not forgotten Rue who helped keep her alive and gave her comfort. She has not forgotten her mercy killing of Glimmer after the attack of the tracker jackers. Katniss still has unfinished business with the capitol.