Whats wrong with her? and why am i being like this?

My Fiance sister has hypo thyroid but also consumes Large amounts of food. She wears a 16 women and 11 shoe and just turned 9. She eats the whole container of General tso chicken . As well as Adult size plates at dinner. She's also about 5'2. And one time I baked her a cake and she ate the about 3/4 in the matter os 24 hrs. Her parents basically let her eat what she wants n her mom orders fast food A lot! Or when she do cook its fried with no veggies @ all. Long story short she had darkening of the neck pretty bad where she's light skin and her neck almos going downward. To the starting of her bak is do dark it looks almos purple ad have a scally type feeling. I recall before the doctors runnin test on her Kidneys they stuck a camera through her mouth to take pictures. His mom is pretty indenial and she wdnt tell us anythng nt even about her thyroids (but its visible and we knw its genetic bc she has hyperthyroids) when she ate the whole cake that time I wud ask her what wud the doctor say she said diet n needles. so ever since her surgery her mom buys Cranberry juice (she sd its senestie for her stomache) so she never ever EVER. Drinks water jus that and grapefruit. And her mom bleaches her neck trying to lighten it bc she's very light n her neck is like flavor flav colo while she's jennifer lopez complexion. An yesterday she fell outside n her mom took her to the hospital I asked did she bruise it she sd no its sore.but my mom says when diabetic u have to be careful because of bloodclots. Any suggestions on what maybe the problem ? And to top it off I'm gettn married n I feel like I jerk bc for some reason ijus dnt want her apart of it , idk wether its this or what but its how I feel.she's a shy kid but when it comes to food its like out the window. And she has a really big hard. Belly and she walk with her stomache sticking out . ( like some pple with big bellys wlk) idk Smh sigh. I am thick as well( about Queen lahtifah size jus with more hips )