Not a valid reason to put a curse on a child still lmaoo. My guess is a boiler plate traumatic backstory about being poisoned or her parents being overly strict raising her to be a queen and she turned out the same way or some nonsense that equally is not a valid reason to curse a child lol
Maybe the queen has a potential to be diabetic and her child can inherit it, that's why she is strict with her consumption of sweets. (=・ω・=)