Sorry I should have offered more info. Right. So we're pretty relaxed when it comes to sweets, DH and I absolutely love sweets and buy them on weekends for the whole family. We'll often do family movie and there will be haribo, popcorn, etc. DD goes to town with friends and they get McDonals, then treats, all fine. What I am finding is empty packets of sweets that she has been eating in addition to all of the other sweets, and in hiding. There will be food that she's eaten and then hidden the empty wrappers under her pillow, in her wardrobe... Everything in the kitchen is up for grabs, there are no restrictions. If DC want a snack they can have it. Food is healthy and cooked from scratched most days, once or twice a week there will be pizza or whatever goes type dinner. I don't restrict portions.
The being grounded is because she has been asked to keep sweet consumption under control which mostly means to not buy them during the week, but also not to take food into her room, as she has left leftover muffins, cake etc stuffed inside her drawers where they have caked against the furniture.
Despite multiple conversations, making snacks available (did a big shop of the fruit she asked for, yogurts, crackers, nuts, seeds, pretzels... she continues overeating sweet stuff, eating in hiding and then hiding the evidence, stuffing leftovers in places where they damage property.