They said on the local K.C. news last night it was a "small caliber" round.
Also showed the cars rear window shot out.
I'm guessing a .22LR or .25 ACP hit the window, lost all its energy on the glass and/or flattened and bounced / stuck in her hair.
It also appeared she had a heavy hair clip under there to hold her hair in place.
At any rate, there wasn't enough hair there to stop a large caliber bullet going at a full-tilt boggy.
rc