I'm assuming besides working out she carb depletes for several days and takes laxatives?
They train for it by water loading to expand their stomach for a day or two before they eat like that.
I watched a documentary on competitive eating and they all more or less do the same thing.
Most of them don't purge the food out, as many contests won't allow it.
There is this Asian chick who is like 100 pounds and destroys almost everyone. I watched her eat like 100 wings in a matter of minutes.
It's a disgusting "sport".