Is my friend preoccupied with weight? Is her anorexia serious? Is she not confident enough?

So she's doing a paper on anorexia and then she was talking about getting her braces tightened and was like "I won't be able to eat much! not that I do anyway" I asked if she was anorexic and she confirmed it, I think she isn't bad because he isn't malnourished looking or anything. But is this serious, I don't want to interfere because II said I would tell anyone. Also she seems preoccupied with weight (I'm kinda fat) she commented on how a girl from our cheer squad is friends with someone slightly overweight and how fat people are never popular. She also said how her ex got really fat after they broke up (or before). She will never try anything new, in cheer practice she would always sat how something was too hard before trying it, we were both new but I would try what ever our coach said to. and She was afraid to tell our gym teacher she had a dentist appointment until I literally pushed her to him. Is she suffering from low self esteem? we aren't the best of friends but should I be concerned and what can I do with out being weird if we don't talk much outside of school?