Yo there is no way in hell she can eat all that shit and keep that body tight flat. She would have to work out more than 4 times a week lol.
Some people have absurd metabolism regardless of anything. Like me. Especially in my teens, I could eat just about anything and NONE of it showed up on my body. Metabolism burned all of it. It's because I had tall genes and grew like a fucking weed at the time.
However, my metabolism hasn't calmed the fuck down since, even a couple decades later. I'm still able to eat a fair bit and none of it seems to stay on my person. To be fair, I have a 6'7" frame to feed after all that growth during my teens, so maybe that's part of it.
For reference, I've barely had to exercise to maintain weight at any moment in my life. Most of my free time was spent sitting in front of a computer playing video games for huge chunks of my lifetime. And yet I still could burn through mountains of food with my metabolism like it was nothing. I'm still a freaking lanky-ass giant with virtually no body fat.
My point is, Anna has amazing tall genes, and it's possible that gives her an absurd metabolism that burns through tons of food to feed her growing young teenage body. Would certainly explain
why she's so gluttonous, too: She may well be hungry almost all the time.