I asked the name of the disease and questioned the fact that the lady gains weight with a calorie deficiency diet.
Every reaction in the body requires a strictly definite amount of substance and energy, each cell spends a strictly regulated amount of the same on breathing and metabolism. Slow metabolism is a myth. There is no and cannot be in the world with our laws of physics of the ability to add weight (even retain) with a lack of calories. Otherwise, they would have long developed hypereconomic engines on the principle of the fat girl, bringing you to Mars on a glass of gasoline.

You don’t think of one thing, sweetheart. With a serious and constant calorie shortage, the prudent body will initially minimize vital activity (to survive the hunger time somehow), and only then will start to eat the reserves. Thus e. Poor fat grandmother (I quote your ham statement) will not be able to go to work at first and will have difficulty getting even to the toilet, and only then will start to lose weight (at the same time the body will first eat the unnecessary muscles and only then will be taken for fat). It is unlikely that the girl sets the goal of becoming a thin ruin. Read about the effects of prolonged calorie deficit on health and the psyche (there were good studies during World War II) and calm down with your hunger.