After Boggs dies during their mission in the Capitol, she demands that Katniss give her the Holo. Katniss lies to her and says that President Coin authorized her to take charge and to lead a mission to assassinate President Snow. Cressida supports Katniss' lie which seems to help convince Jackson to allow Katniss to take charge.
Jackson was assigned to be a soldier in Squard 451 as a sharp shooter with Katniss, Finnick, Gale and other soldiers. Jackson kept the team under control and often gave them orders. Jackson helped Katniss recieve the task to guard Peeta during the night. She helped Peeta with his memories by playing "Real or not real" with him so he knows what is real and a lie. Jackson argues over the ownership of Boggs' Hoo which he gave to Katniss. Cressida backs up Katniss and Katniss tells her that she is on a mission from Coin to kill Snow quickly so the war can end. She witnesses the broadcast that leads Panem to think that the squad members are all dead.
Jackson and Leeg 1 sacrifice their lives at the meat grinder pod in order to hold off the lizard mutts and allow Katniss and the other members of the team a chance to escape. Later Katniss regrets having lied to Jackson and inadvertently getting her killed but Cressida reassures her that Jackson knew they were lying but wanted to push forward with the mission regardless because she trusted Boggs who clearly wanted Katniss to go on.
Jackson is a middle-aged woman who looks kind of sluggish. She is farsighted which gives her the advantage of being able to shoot things that the other members of her team can't see without a scope.