She seems to hate herself and have very low self-esteem. Eating disorders are common on many college campuses across the country, and are quite difficult for both the sufferer and her or his friends and family. Above all, approach your friend from a stance of support, caring and concern, rather than accusation.
People react poorly to being told they have a problem.
Confrontation can be caring, however, if you merely point out behaviors you've noticed. Help improve your friend's self esteem by noting good things about them, real ones, and by reinforcing positive self-statements. Both places have non-judgmental humans who listen real well.