Buffy definitely isn't out to get her. She likes Katniss and she knows Derek likes Katniss. Those two things equal Buffy teasing Katniss. It's how she shows love. That's pretty much the thing about being cared for. If someone cares, it doesn't matter whether you want them to or not, they just do.

"Well, that's a start," Buffy says, looking curiously at Katniss. "Cisco Ramon. I haven't seen much of him, but he seems nice enough." Derek invited her to come sleep in the room with them though, so it's likely Katniss will see Buffy back in the bed that she once stayed in before.