Maybe faster metabolism? She lost entirely too much weight in one week though, so more than likely she'll gain it all back, and then some.
What you can do is ask her if she can help you with portion control and see if that helps.
edit; not to mention, most of that weight, if she isn't really exercising, could be water weight and loss of muscle. YOU, on the other hand, I take ARE exercising so you are building muscle.
REIABBY 3/25/08 11:30 P
My sister is eighteen years old and weighed 195 [two weeks ago] now she weighs 185! all she did was eat healthy and ate smaller portions. she worked out like twice out of the whole week for 20 minutes total. shes so lucky, she wasn't starving either. i am sooo jealous! why cant i lose weight that quick?
