Katniss was trying to hunt in the woods, not for her that was rich now but for Gale and his family because he has entered in the coal mines. Hazelle, his mother was in charge now of his tree brothers.
When she came back to his house, she found in addition his mother, the President Snow.
He told her the problem with the berries they used to save both Peeta and herself in the last Hunger Games. Some people saw it not as a love act but like a defiance one to the Capitol. And that it can lead an uprising and consequently a revolution. And, obviously, if this happen the Capitol won't think twice to kill Katniss and everything that surrounded her, including Peeta and Gale. Not this to happen, the president told her to make everyone believe it was just a love act during the Victory Tour when the winners will have to make a visit to each district.
Once in the train, Haymitch told Katniss that Peeta and her will have to be together forever, ever get married, since the Capitol will always check their private live. And also they'll have to do as mentors in the Games.