Do you think this is normal for a teen?

I have a friend who wants to become a glamour model. She is so exicted about it and so was i until...She used to weigh 78 kgs and 5'6 then she went on a very nice diet ( i admit) and reduced to 48 kgs. I am really worried though i must admit she is really looking nice but is this normal because i really do not want her becoming anorexic or bulimic. Is this okay for a model? Is this normal weight for a teen?