While I don't necessarily disagree that she's suggesting a desirable diet, the logic behind the specific suggestions is complete BS.

Here's a list of the NO food:
cheese, etc. - breaks down into sugar

Cheese is essentially carb-free, so only "breaks down into sugar" through gluconeogenesis - and if you're worried about that, then you may as well strike all proteins from your diet.

Here's a list of the YES food:
citrus fruit, melons, berries, cherries, pineapple, bananas

You can ferment all of those things on your tabletop. Heck, orange juice and fresh pineapple ferment just fine in the fridge, and contain detectable alcohol even when they don't taste "hard."

yams, sweet potatoes, and dark chocolate (60% or greater).

Sweet potatoes convert to alcohol, too. (In the lab, at least. In the body, unless you've got a massive Candida overgrowth, there's not that much endogenous ethanol production.)

60% dark chocolate is 37% sugar by weight - 16g of sugar per 43g of chocolate.

Bodies (and brains) are weird things, so it's entirely possible that you'll see positive results from that diet. But not because you're avoiding "foods that could convert to alcohol."

If I were trying that diet with my kid, I would be very, very careful to ensure that she got sufficient calories. It has the potential to be low carb (unless you *really* love quinoa), and low carb is great for hunger-free weight loss - which makes it hard for a kid who eats when hungry to eat enough. Really push the fats - no lean meats, oil on the veggies, etc.