It's prevalent in poverty stricken homes, as well. It comes from the knowledge that there is enough to eat for today, but uncertainty about the future. It's called food-insecurity, and parents can actually pass it to their kids by talking about worries about feeding the kids, or things of that nature. Or in food stamp families where the first few days of the month are full of lots of snacks and treats, and then turns to meals only, or less, later in the month when the funds run low.
In our case, we make sure that the kids are all fed the same amount (as close as possible) every day. Breakfast, morning snack, lunch, afternoon snack, dinner, and sometimes a small snack before bed if dinner gets served early. I do sometimes have to lock the cabinets or the fridge, but I try not to, since I worry that might make it worse in the long run. My middle son hoards because when he was little, between 6 months and 2 years, he had incredibly bad allergies to almost everything. he was not allowed most of the things that other kids get, including cake, dairy, candy, even most flavors and dyes. Now that he has outgrown most of the allergies, he seems to think we kept all the good things from him to be mean, so now he hoards them. i think he's afraid of us taking them away again.
My older son hoards because he wants to. Period. it's a behavioral thing. He knows that he can bribe his brother and sister to do his chores or clean his room for him if he has a candy stash to offer them, so it's like currency to him.
They aren't underfed, and having grown up in a household that could only afford two meals a day most of the time, I promised them they would never go hungry, and I meant it. They don't. But they do have food insecurity, passed on by me when they were younger. You think that a 2 year old won't remember that there were days he ate, and Mommy and Daddy didn't, but they remember.
Kids can be deeply impacted by many things, and with mine, simply seeing hunger, even though it didn't touch them personally, that's what happened to mine.
I feel so bad for this girl, because I did grow up in a house where there wasn't enough to go around, but somehow it was made better by the fact that i knew I was loved and that everyone else was suffering along with me. To not be offered that comfort, but instead to know that you are the only one suffering, must have been terrible for her. With holding of food in an abusive way is one of the worst things that a parent can do to a child, in my opinion. I would rather be beaten than starved.