Ok Y., I've got a ton of information to share, bare with me because it might be pieced together a little hap hazardly!
Yes, Heather is right, Chromium deficiency can lead to sugar cravings. And ingesting sugar depletes Chromium. Sugar also depletes B vitamins, Calcium, and I'm sure many others.
Dehydration causes sugar and carbohydrate cravings, and ingesting sugar causes dehydration.
It is by no accident that people are hooked on sugars and processed carbs. These foods are laced with chemical additives that the food industry KNOWS are habit forming. Processed foods of all kinds (including sugar which is a processed food) have become a trillion dollar industry and they have made sure to keep you coming back for more.
When these foods get ingested they not only displace the food that would normally supply the nutrients but they actually destroy vitamin levels and create chemical havoc. Your body starts to weaken and break down from malnourishmet. Every biological system in your body is taxed. Once malnourishment sets in, you are a sitting duck for every opportunistic pathogen and parasite to come along. (this is exactly what happens to potted plants that don't get watered. Next thing you know, they have scale, mites and fungus.)Your body, in a state of survival mode, will start sucking water, chemicals and nutrients out of bones and tissues to supply vital organs like the heart and brain.
A common parasite that has become a huge problem and infects a lot of people is candida Albicans(fungus.) Candida can send out signals to the host's brain - cravings for the food and chemicals which allows it to flourish. Malnourishment in our body also sends out signals to "eat." (fat people are malnourished) Extreme thirst can send out signals to eat. The primitive body was set up that way, before chemically altered food was made, to make sure of it's survival. "real" food can supply water to a dehydrated person who wasn't near a watering hole, especially fruit and veggies. If you keep filling the signal with poor food, you body will keep sending the signal, until it's needs are met. Your body also strives to maintain a certain chemical balance, blood sugar, etc.
To truly get those sweet cravings under control, you will have to drastically reduce or eliminate the carbs from the diet and start eating a diet of veggies, nuts, beans, eggs, fish, butter, and protien. Although there are pills to help with cravings, no pill can take the place of what a good diet can do. At some point, when the body is more healthy, she can go back to eating fruits. Chemicals and additives have to be stopped as well. No dairy (a dead food unless it's raw anyways and it feeds candida), MSG, soy,yeast or yeast extract, soy protien, hydrolized veg. protien, textured protien, hydrogenated shortning, aspartame,...you name it. Buy "God made" foods with no food labels on them. No Sodas /juices. If she wants a sweet drink put lemon juice in a glass of water and add Stevia.Lemons detox the liver.
Take L-glutamate to restore gut and lactobaccilus to restore flora. Since B vitamins are paramount to the nervous system, A liquid b vitamin complex under the tounge 3 x a day should be taken. Oregano oil under the tounge can work wonders for candida (and sweet cravings) but sometimes it can be harsh (a burning sensation) (depends on the brand)and some might refuse to take it.
If you must, you can look for ways to make her low carb diet easier by allowing some sugar replacement.
One subsitute for sugar is Stevia (Trader Joes carries it)which will not affect blood sugar levels. It is made from leaves and is found in a powder forn at TJ's. At first it can seem funny, but after you get used to it, as with anything, it becomes more palatable.
Zylitol is a 5 carbon sugar alcohol from the bark of birch trees that cannot be metabolized by candida, is slowly absorbed and has a GI of 7 (table sugar has 100.)It's actually very tasty and can be used the same as sugar, but it won't "brown" in baked goods. It can be useful for diabetics because no insulin is required for metabolization.
Two other things I would consider is fulvic acid for thyroid support/cellular support/recolonizing the GI tract, and chia seed can be used to stabilze blood sugar.