I'm not sure if you already talked to her or not, but i didn't see this thread before..

Im 5'6, and i weigh 106 pounds.. I eat and everything, i mean i eat.. But i just don't gain weight. Period. I'm not anorexic or bulimic, i just don't gain weight.. If you ask her you might hurt her feelings. I know if someone asked me that i would be hurt, because i am skinny, and i hate it.. So if you aren't almost positive i wouldn't ask.

That's just my two sense.