Not neccessarily. Especially at this age, girls tend to have issues with self-perception. My first year in college, there was a girl living down the hall who everyone knew was anorexic. Her parents would come visit regularly to try to make sure she was eating, sometimes taking her out to one of the local places to have lunch together or something. I've also seen a few of that type at the campus gym. There're plenty of social pressures to look trim and it can lead to eating disorders. I guess the other questions I would have is how her grades are, and has she made friends?
Good grades, lots of good friends.