Susannah>
Anorexia nervosa is a psychiatric diagnosis regarding one particular type of
eating disorder. Anorexia is simply a loss of appetite, which might accompany a
variety of illnesses or might be a side effect of a medication. Not knowing
your co-worker's daughter, it's hard to tell which one it is. It very likely
could be anorexia nervosa. I think someone did describe anorexia nervosa
earlier. If you have access to Google, you could do a keyword search and find
all kinds of information.

"She was very healthy, she ate well and played sports"

Teenage model dies six months after anorexic sister The death on the catwalk of a young woman who followed a starvation diet failed to deter her younger sister from pursuing a modelling career.

I didn't know there was a distinction.  A co-worker's daughter was diagnosed
with it recently.  All he said was "anorexia."