How can you lose 10 pounds every week?

Ok. my 11 year old sister is reapeating and reapeating and won't stop reapeating that she is FAT!!! She weighs 140 almost. Well, She wants to be 90 pounds by the end of the summer. So like 7 0r 8 pounds a week. please. and she wants to lose it naturally. not by machiane or those food things off of tv. she wants to cut back on her eating and stuff. like how much does she need to eat, how many sit ups how many push ups. she can't do chin ups. not even i can do that. ha. well do ya get it. How many minutes she needs to run. how much of everything she needs to do everyday. All that and more. what ever you can think of. please. i think if i have to hear her say anything else i will SHOVE A SOCK DOWN HER THROAT OR HIT HER HEAD ON A BRICK. please, any thing is good. thanks and by