In the commentary, Tina Fey notes how surprisingly moved she is by it.
Even though they play girl politics with each other, glimpses of Karen and Gretchen's true friendship show through. At the Halloween party when Karen can't figure out how cousins work, Gretchen patiently explains things to her and gives a sympathetic "oh honey" where everyone else would have called her stupid and put her down. Likewise, when Regina calls Karen a slut, Gretchen's first instinct is to tell her rather than trash her behind her back.
Karen overall seems to be a good-hearted girl, aside from occasional moments of bitchiness. When Regina is sad about her break-up, Karen suggests Taco Bell to cheer her up. And after the "Jingle Bell Rock" scene, Karen hugs Cady for saving the performance and says "that's the best it ever went". Cady even seems to feel sorry for her after Regina calls her stupid.
In the end scene Karen is seen near Cady's group of friends, implying they remain close or at least cordial.
Cady's Spring Fling speech. "Everyone looks like royalty tonight."
When Cady apologizes to Ms. Norbury for putting her in the burn book for selling drugs. Also, it may not be as much, but when Aaron Samuels tells Cady "welcome back, nerd." This shows that the others are seeing Cady progress from the plastic she used to be.
Cady making up with Aaron, Janis, and Damien at the Spring Fling after her speech.
In a way, Reginagetting her happy ending is oddly sweet. She learns to channel her rage into sports, and joins the lacrosse team. And since the lacrosse team isn't scared of her, they're actually her friends, not just using her for a social status or going along with what she says because she intimidates them. We see her scoring a goal in lacrosse, and the rest of the team dog-piling her, and at the end, we see her with her teammates, looking like she's genuinely happy. Her dose of Character Development did her good.
It is rather sweet to see Janis happy while kissing Kevin in the finale. When She Smiles indeed.