The hardest part to accept is that girls are likely going to be influenced by what they see--and more importantly, what their peers are doing--no matter how much you praise their achievements, surround them with people who have solid self-esteem and keep them active so that they understand a body's functions and the importance of being strong and healthy. Sometimes we don't realize we're modeling negative messages through our diets, for example, or our own self-image (if you don't like yourself, your daughter will start picking herself apart, too).
My daughter is studying ballet fairly seriously; naturally I was concerned that body weight was going to become an issue and she'd worry about being "too fat". I just keep saying how different girls have different shapes, some have spines that arch just as others can do splits in both directions, etc. I try to use stories that illustrate acceptance and courage; finally I just tell her I understand that she wishes her legs were longer, her hair were blonder, etc., but that she would continue to change and appreciate what she's capable of doing. I used to wish I had what other girls had, but what I didn't know was that they were wishing the same thing about me.
Keep at it. Your daughter will hear it. I'm also fortunate that my daughter's school is doing a session on media literacy and how imagery affects self-image. And this might surprise some people, but American Girl has an excellent series of books on every issue a girl might face in her pre-adolescent and adolescent years. My daughter often refers to the Body Book, which is laid out in chapters according to developmental stages; there are also books on dealing with conflicts between friends, dealing with a parent's divorce, understanding how different relationships have different meanings, etc. Two thumbs up!