As a mother (or father), you have the opportunity to be a very rare breed of parent - the kind that actually empowers instead of enfatties her child(ren). I can't even begin to tell you how many young people I've come across who struggle with eating well
[and being active] because their parents have control over what's available
[, are not providing the best example] and simply don't care enough to make an effort.
If there's nothing but good, healthy food (see: Berardi's 7 habits) in the house, you don't need to be worried about setting an example or anything. Just live what you would preach to her. Osmosis will do the rest. And everyone in the household will benefit. I wouldn't even say a damn thing about "weight loss" or anything of that nature. Simply put the emphasis on eating good foods. By not leaving her a choice in the matter. Control what comes into the house, and you've won 80% of the battle for healthy living. The proximity defense, they call it. In many cases, eating according to a Berardi-style template is enough, with no regard for calories. (It's pretty damn hard to overeat on nutritionally dense but calorically sparse lean meats, vegetables, and fruits.) Particularly for young people, as they're still growing. "Snacks" and "desserts" become things like dried fruit and nuts.
With time she will learn to like clean food better than the more aggressive-tasting garbage she will occasionally be exposed to at school and by friends and such, and will make the right choices on her own.
What I'm saying is, this should be a very powerful motivator for you to do your very best to get and keep your **** together. For yourself, for your daughter or son, for great justice... and maybe even for me.
Every time you go to buy or eat junk, think about how you want to be remembered by your child(ren). If you care hard, you will make the right decision 98% of the time.