Carrie decides to leave Todd at the daycare, after all, his fate was well deserved.
She starts walking around town, hoping interesting oppertunities will pop up somewhere, then, she spots a elementary school, and decides, what better place to go to? She's sure to find some interesting oppertunities here, perhaps a bully that she can humiliate, an asshole teacher she can regress, or just generally swap people around to cause mayhem, it's simply too good to pass up!
She decides to make herself 9 so she can fit it, not the oldest, but not the youngest, in the middle, really. She changes reality so that she has always gone to that school, and manages to find her classroom, just in time for the first lesson.