My guess is sucking in, plus some sort of control from the garment, which looks to be some manner of bodysuit bustier tucked into jean shorts. In the accident photos, she's not wearing a bra and I am not even sure she's got underwear on under those ragged-ass shorts, plus she's lying prone and we all know that isn't usually a flattering position for flab. ;)
Further, it is highly possible that she's had both muscle and internal organ displacement from the accident trauma. Some of the excess gravitational pull on that gut may actually be because some of the tissue inside it is not actually sitting where it is supposed to be sitting.
Vedderman I like you. You're informative, yet respectful. Class act.