I would assume they feed her several days ago so that she wouldn't have a full stomach for her trip. Kings are such aggressive eaters (and mine seem more likely to have an attitude when they are hungry) that the usual advice of waiting a week before feeding is not as big an issue with them - in my opinion. Actually all of my colubrids, I feed them the day after bringing them home.

Mine love to burrow as well - sometiems they'll use their hides. My Cal King is on paper towels for now and my Mex Black King has just been moved to Bed-A-Beast for some burrowing fun. He seems to really enjoy it. You can use the hides to weigh down the newspaper or consider giving them a loose substrate so they can just burrow to their heart's desire.

I got my Mex Black when he was about 8 months old....I'm trying to remember what the breeder was feeding him - I think pinkies, but I can't remmeber. But my guy was pretty thin for his age (according to my vet who used to breed them and others that I asked on different forums). My vet said some breeders just feed them a maintenance diet with the intention of selling them. He had me start feeding my guy every 5 days to fatten him up a bit. You should be safe with the 'feed prey equal to the widest part of their body or up to 1.5 times that width'. Just feed her a second or third one if a single one seems too small. She'll love ya for it. Any pics of her home?