At this age I'd concentrate more on her sense of self-efficacy and self-worth (not self-esteem, which is a different thing and not really that useful because it doesn't come on its own without the other things first!).
I recommend Sleep Talk, by Joanna Golding (that's definitely her surname, anyway!), if you're stuck, and even if you're not stuck Positive language you can learn from looking up Neuro Linguistic Programming (NLP) sites and strengthening her from the inside.
I would caution about focussing on positive body image, because that's externalising her worth, still - it comes from inside and her life satisfaction will depend on how she can draw on her inner strengths, not on doing her best to continually remind herself that her body is fine. This will come, and again, on its own it doesn't have the strong foundation it could otherwise have.
Don't be afraid to ask people to cease and desist when they start talking about bodies and food intake. My mum doesn't like being reprimanded, but I actively change the subject when she starts praising my kids for being 'skinny' - I HATE this with a passion, and will always have a word to her about it, because she's doing to them what she did with me as a kid with her value judgments and praise. She'd compare me to other people (favourably, but I hated it and no matter which way comparisons go they are so, so destructive!) and it made me think about these things A LOT. (Not that I think you've been doing this at all! Just explaining my POV )