Someone missed the entire point of Mockingjay. All of your realized horrors are horrors for a reason. None should be changed and they are set up that way intentionally. Prim’s death was the most important thing in the book. Katniss’s entire reason for volunteering as tribute (and the massive snowball of events that followed) was to save Prim, and in the end the very events that happened due to her entry into the hunger games led to Prim’s death.