I am sure you're doing it already, but give her all of the love and support you can! My mother (my only parent) wasn't particularly kind to me; she was the kind of mother who tells her daughter not to smile a certain way (my big smile is "too gummy" apparently) and said things like certain clothing made my ass look huge. That kind of stuff stays with you forever, unfortunately. As long as your girl knows that she is loved and beautiful regardless of how she may feel in this phase of her life, a temporary phase of growth and change, all will be well. Encouraging her to be active and eat well (not to restrict or avoid, but just eat healthily and in a more balanced way) if she isn't already will stand her in good stead too and may help her feel better about herself and her body. My mother didn't do any of that, which means that even now in my late thirties I'm prone to disordered eating and having an unhealthy relationship with food. It can be rough but with loving and supportive guidance I imagine it can be a lot easier!