Johanna won the 71st Hunger Games by pretending to be weak and that made all the other tributes leave her for last. Then she unleashed her full potential and violently killed all the remaining tributes.
Johanna, being the only remaining District 7 female victor, was Reaped for the 75th Hunger Games. She was approached by Haymitch before the Games and joined the rebel alliance. She, along with Blight, resued Beetee and Wiress from the bloodbath. They then travelled into the jungle and got caught in the blood rain, which caused Blight's death.
Johanna took Beetee and Wiress to the Cornucopia where they found Finnick, Peeta, and Katniss. Eventually they found out about the clock themed arena and while they were distracted, Wiress was killed. Katniss killed Gloss and Johanna threw an axe into Cashmere's chest.
After they had made a plan to electrocute the food in the water, Johanna and Katniss took the wire to the lake in the middle of the arena. The wire was cut about halfway by Brutus and Enobaria. Johanna pretended to kill Katniss and dug out her tracker. She then led Brutus and Enobaria away from Katniss and they followed Johanna.
Johanna was captured by the Capitol but was rescued by District 13. When she came back she had hydrophobia, or fear of water. Johanna was not present in the invasion of the Capitol because she could not overcome her fear of water.