Alternatives to foods, white pasta to brown pasta, white bread to brown, potato to sweet potato, simple small changes can make a big difference at a young age, fizzy drinks carry alot of sugar.
The suggestion to involve her in the cooking progress sounds great, if she is good with eating veg, portion size, half the plate veg, a quarter carb and quarter meat, try plating on smaller plates, plates look full so portion size looks bigger but isn't,
And for exercise, u don't even need to leave the house for this, half an hour each night, try things on youtube like dancing and u join in with her, make it fun and not seem like exercise, make it playfull and enjoyable,
It's a touchy subject esp for girls that age, I would fear it going the other way and her avoiding food altogether.
My mum used to tell me it was just "puppy fat" and it would go away, it never did and I do wish she hadn't had so much treats on hand that I then abused, I am now doing the opposite with DS, and starting early on it,
Hope it helps, good luck xo