Like the other ladies said, kudos to you for wanting to make sure you set up your DD for success in living a healthy life. Diet plays an enormous part in our health, so to me, taking stock of what you (because your kids watch how you eat) and your child eat is number 1. No junk in the house is the first step - if it's not there, you aren't tempted and therefore your child isn't either. If you can in the most part avoid using food/junk food as reward for good behaviour you will be avoiding that trap for a lifetime for her. that doesn't mean you never have junk food - but rather it's an every now and again food. The message is not that it makes you fat, but that it makes you unhealthy! Running around at school and extra sports is part of it, but that alone won't be enough without a great diet. Ditch sugary treats, chips etc for a once a week treat to start with, shared with the family. Check out the backs of packs to see if they have numbers written on it - a great start to realise what kids are eating - and therefore what to avoid. No processed sugars and no trans fats is far more important than food advertised as 'low fat'.
I am not naturally fat, however I eat much better than the majority of people do and think often people don't realise what they are consuming. Good luck. On your journey - I hope you can make the changes for you as well as your daughter