Good job wanting to make some changes for this family!! I'd make the changes slowly though, if her system is used to this junk, it might shock her system to have all these healthy changes quickly! I would switch out the milks an yogurt, and then start including fresh fruits and veggies with her snacks, and cutting back on the amount of junk a little bit every time so that she doesn't refuse the changes.
I'd also avoid having snacks all the time! For my kids, if they snack all day, then when it comes to meal time, they only eat a little and avoid the veggies! I really only do one or two of snacks a day. We'll do breakfast: eggs or yogurt & fruit or oatmeal with a choice fruit & nut toppings (they love having the dishes set out and getting to decide what to mix in) Just be cautious with nuts at her age. Usually I skip snacks until after lunch. I'll do raisens and pretzels, or dried cranberries and a graham cracker. Their favorite though, is to go out to the garden and pick their own carrot! wash it with the hose and munch away!
Speaking of garden, one of my kids favorite activities is to halp in the garden, they LOVED planting seeds, and watering, and watching the things grow. I would definately include her in your garden plans! It will probably encourace her to eat more of the veggies if she has a hand in growing them.
Good luck and good job!!