Why Kate became enemies with Lizzie, Gordo, and Miranda.

The development of a bust lead to a newfound popularity, which in turn fed an underlying desire on Kate's part, thus she ditched her old friends and her old life to continue to hold onto her new ephemeral existence.

One will note that Kate's 'popular girl' veneer cracks in times of stress, and as certain episodes note, the old Kate, the real Kate, is still in there.

There were only two long term storylines with 'Lizzie', and the Redemption of Kate was by far the biggest one. 'The Lizzie McGuire Movie' sped up the reclamation of Kate's good side with her helping Lizzie. One can not but believe that once they got back stateside that their dynamic had changed.

I guess what they're saying is, she hit puberty and started to become pretty. She got more confidence, more friends and ditched her olds ones. It's not unheard of, but the show glossed over it.

Kate's personality fluctuates throughout the series between who she really is, and who she's pretending to be. She pretends to be mean to intimidate people into liking her, or from standing up to her. I always thought she fought with Lizzie the most because Lizzie knew who she really was, and that bothered her. And you can see through the progress of the show, Kate actually likes Lizzie and even helps her out a few times. I feel like by the end of the movie (the series finale) Kate kind of goes back to herself, and even surprises Ethan by eating spaghetti. Something she wouldn't do.

-Who is it?
-It's Grandpa. And it sounds like he's gotten into the horseradish again.