How did rue die Hunger Games?
Correspondingly, who killed Rue in The Hunger Games?
Katniss came to her rescue, but Marvel speared Rue in the abdomen. In the ensuing conflict, Marvel was killed by Katniss, who was trying to defend Rue. The dying Rue told Katniss she had to win and asked her to sing for her as she died.
Keeping this in consideration, how did rue help Katniss in The Hunger Games?
The Hunger Games Rue is able to hop from tree to tree like a squirrel, a skill that helps her outrun and evade her competition. She tips Katniss off to the tracker jacker nest that saves Katniss' life. She wants to make sure that Rue's death will not go unremembered.
Moving onto the events of Mockingjay, in the aftermath of Peeta's torture, he gets hijacked by the Capitol and makes Katniss out as a target to kill. Johanna, however, during her time at the Capitol, gets soaked in water and electrocuted — which I imagine is about as bad as it gets.