Look at it from the kid's point of view. She is trying to do what is healthy and your friend is forcing her to eat things that she believes are causes her pain (and they probably are causing her pain).
Not only will your friend screw her up physically, she will also give her psychological issues.
In all of the universe there is only one person with your exact charateristics. Just like there is only one person with everybody else's characteristics. Effectively, your uniqueness makes you pretty average.