The air isn't cold anymore--it's freezing--and she shivers a little and thinks her hair is a mess and she's on her way to classes and the guy in the truck she just passed definitely looked at her like an escapee from a white padded cell. But the small, finiteness of shivering with cold and the uncontrolled nature of her hair and expression seems to perfect the moment somehow.
She grips the wheel with slightly-numbed fingers and turns her eyes to the road, her mind running wildly through a field of swaying grass.
She's shaking with cold. She's never been warmer.
I like this a lot. A lot; did I mention that? It gets a little unruly and untamed in the paragraph starting with "The air isn't cold anymore..." but you recover well at the finish. Really good, Ana.