Katniss needed to think about how to answer that question. "Uh, officially, about five months," she said. "But we were friends before that and..." she shrugged. It had taken a bit of time for them to actually talk about their feelings and put a name to their relationship. "She's great. You'll have to meet her."
And she would have to warn Su about Effie's... eccentricities. "I also have a young woman named Mitsuko who lives with me and Prim. She's become a sister to us. Her world is similar to ours." Bonding over trauma was a hell of a way to meet people, but it worked.