well, on the photo on your profile, she doesn't look overweight, but I am assuming she has added since then?
My ds1 is similar. He is a very big (tall) and broad shouldered lad anyway, but has the real potential to become overweight. It is a constant struggle to hold him back.
We don't have ANY sweets, crisps, biscuits or indeed any 'grab-it-and-go' food in the house, except fruit. - Until recently, we did have a treat jar, where a sweet would be authorised from time to time. However, this came to be abused (little sneaks!) so it has now gone!
We keep the bread in the freezer, and just take out slice by slice what we need, this stops him going and grabbing bread.
The only cereal in the house is weetabix and shredded wheat.
We only have wholegrain bread - he used to eat far much more bread when it was white. Skimmed and semi skimmed milk instead of whole, and so on.
Things like cheese and yoghurt, which would be very tempting to overeat but are still essential for a child to have, in proper proportion, we buy tiny amounts several times - I will buy 2 yoghurts on a day I am going to give them a yoghurt, smallest cheese from cheesecounter instead of getting a pack in etc etc
I now do fruit salad and keep it in the fridge, same with carrot sticks. Not HUGE amount, but a good portion, so even if he ate it all, it would be ok.
I talked to the school and the lunchladies give him a slightly different portion of food - I asked them to steer him towards the most healthy option, but if he really wanted the pudding instead of the fruit/yoghurt, they were to give him half a portion. They do this and so far it is working well.
Instead of icecream (he still gets treats!!) it is frozen yoghurt or sorbet or ice lollies. He doesn't even notice! (although we did have an incident the other day when the whole pack of ice lollies got snaffled! So there will be no more for several shoppings!)
He still gets a few sweets now and again, sometimes I bake a cake, or take them to Mcyukkies (I know!!) but all things in moderation and the day in day out changes I have made balance it out.
Plus, dh takes him walking, park, plays football with him, swimming etc as being active is just as important.
I tell you something, he bloody HATED it at first - as I recall, the switch from white to wholegrain was one of the hardest for him, he REALLY kicked off! But over time he has come to accept it.
Sometimes he does, even with all this, get a little round and when this happens we look at ourselves and realise we have got a bit lax, we retighten and off we go.
One other thing we do, is make most of his trousers nonelasticated waists. This way, we can see very very clearly and quickly, any weight gain.
I am also always trying to learn about the best options. And get surprised a LOT! Only recently I was told that low fat spread is not as good as butter! I didn't know that, so now I use unsalted butter (in tiny quantities).