Sounds like she has me to flu. She needs to up her salt intake. Pickle juice should help clear it up.

I'm not sure keto diets are good for kids, but I can tell you (because I do a low-carb sort of thing) is that the loss of energy and headaches is the body's way of craving carbs (especially if she ate a LOT of them prior to doing this). Also, she may have some muscle cramps -- mostly legs, because unless she supplements she will take in lower amounts of magnesium and potassium.

Non overweight 12 year olds should not be on any kind of diet.

Actually I do...I work with women over 45 who have physiological fat loss issues and a ketogenic diet has worked very well for most of them, not just to lose weight but for healing the body in many areas. Several of them do incorporate this higher fat way of eating for the rest of their family with good results.

I also use this way of eating therapeutically with my clients that are working through Lyme and Mold issues and have no need to lose weight. Having said that, the most important thing that comes into play with diet is: you should eat the best way for your body. Period.

Diets, per say, are garbage because they don't support a person finding the right way to eat because they are not designed for the individual, they are designed for the masses. Whether she eats keto, low carb, vegan, etc, it is just eating and it may or may not suit her. Keto is not harmful, though, as any human being has the ability to run on fats as opposed to running on glucose. The body will always make enough glucose to support the brain via the liver. No different then eating raw vegan benefits some people but not all. Again, it comes down to what the individual body needs.

Incorporating a ketogenic diet does come with some initial energy loss and headaches as the body builds a way to burn fat for energy and yes, as mentioned above, sea salt works great for helping to balance the needs of the body.

Most important: your SD should thrive from her food choices and switching up macronutrients from one way of eating to another will always bring an initial stress to the body, even if she were to stop eating a bunch of junk food and started eating real food.

I did keto for a little while. I lost 9 pounds in 2 weeks. While that part was great, the way it made me feel was terrible. I also couldn't drink beer which I wasn't willing to give up long term, so I'm back to a lowerish carb/low fat way of eating. Have her drink some pickle juice and take some magnesium and potassium supplements.