How do I tolerate my pig of a niece?

I am currently living at my aunt's house with my niece staying over. Her appetite gives me nightmares. Where my niece lives she doesn't get good food to eat. That's why when she comes here to eat, she hogs on whatever she gets. She is just 13 and fat. Let me give some examples:
1. When I was new here and totally unaware of her eating capacity, she wanted to have Nutella , so I took the biggest jar for her. To my shock, full jar over in a day! I was having ice-cream next day and wanted Nutella with it. ALL OVER. IN ONE DAY.
2. I got a 6 pack of noodles. She finished all of it in TWO HOURS.
She can finish a full family pack of ice-cream in ONE SITTING.
3. Her appetite is HUGE, so I just stopped purchasing such foods after seeing how much she eats when she is here. I don't order in when she is here. The problem arises with me is that.. I like eating healthy in my evening snack, something hot and something loaded with veggies. I can't make it here COS OF HER EATING CAPACITY, it is really scary and very frustrating. I don't enjoy eating snacks like chips biscuits so much, but because of her being here I have no option but to eat that. Ohh, they also finish pretty fast than usual when she is here. I purposely cook slowly so that she eats something to satiate her hunger BUT NO!! She will keep coming in and out and keep asking me "Are you done?" So instead of my usual 3 meals a day, I am living only on 2 meals a day. She makes faces at her aunt when I want to take something and my mum makes faces at me to give my niece the food because it is HER HOUSE. Like my b*tch of a niece already snacks and drinks juice and stuff all day BUT can't let me eat enough lunch or dinner? The problem is my health? How do I keep myself healthy and sane in this scenario and still ensure I eat enough and healthy? Her uncle commented on her eating capacity, she cried a lot. After that day, she was like "I can't eat so much" but eats in the kitchen. I am irritated by her acting.
How do I tolerate my pig of a niece?
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