This is more deep-seated than supportive boyfriend talk. A lot of people have body image issues, and young women are particularly pushed to have them. Advertising and the media really push it these days. Every model is thin, young, and often pale. Westernized features tend to be emphasized. Poses are to look at men in photo shoots, or to look at other women in order to, you guessed it, appeal to men. Read any so-called women's magazine, and they are all about pleasing men, whether it's through sexy talk, losing weight, baking cookies, wearing certain fashions, or acting subservient.
There are exceptions, yes. So try steering her to some of them.
Is she athletic at all? Then try competitions. Maybe she can run? If she can, then finisher medals can be a lot of fun and give a sense of accomplishment (or do you think she would be upset if she didn't win?). An athletic competition is about superiority, yes, but it's not about looks. The prettiest girls don't necessarily win the race, and neither do the thinnest.
If athletics isn't her forte, what about making art? Again, the idea is for a sense of accomplishment in something which isn't looks-based.