Lol. Gooooood question. And one that I actually haven’t really put much active thought into even though I pointed it out. Heh. Let’s see if I can come up with an answer that makes sense.

In early Season 4, I’d always associated Beckett’s buns with the notion of self-containment and rigid self-control. This was most evident in “Kill Shot.” For most of the episode, Beckett was fighting the symptoms of her PTSD, and she kept trying to beat it on her own. There are two scenes where her hair is down. One is when she’s drinking and basically flipping out in her apartment. In this scene, her hair is wild and all over the place, reflecting her emotional state. The second time her hair isn’t in a bun is during the last scene of the episode when she’s in Dr. Burke’s office. This time, her hair is in a half-tail, symbolic, I think, of the fact that she’s learning to let go, but that she hasn’t yet.

That being said, I feel like her up-dos this season have a different flavor from those of last season. Her buns and pony-tails are highly stylized this season which give her character a certain extra sleekness and sophistication. Perhaps that’s exactly what they’re trying to convey. The Kate Beckett of Season 5 is a more polished and refined creature than she was in previous years. She’s learned to handle her mother’s case and Senator Bracken with much more grace and tact. In essence, many of her rough edges have been buffed.