She could actually eat more. Michael Phelps has to down 12,000 calories a day to keep up enough energy for his hardcore training. And he doesn't eat every 15 minutes either, he just eats A LOT when he does. All he does is swim, eat, and sleep, but it's definitely possible.
But yeah, it's actually quite a bit of work for someone who isn't used to eating that much in a day. I could eat a lot more than I'm doing right now (I'm definitely underweight and could use a few more pounds), but my stomach still rebels. My GI tract has not been liking me the past 6 months, and I don't like pushing it.
And if they determine that it has something to do with her thyroid, there are actually drugs they could give her to slow her metabolism down some. But the article isn't too clear about that.