Set the example, do you enjoy snacking with her? What are you snacking on? In my house we snack on things like carrots, celery, cucumbers, grapes, tomatoes, dried cranberries (not crasins), bananas, apricots, nuts, strawberries, blueberries, blackberries, raspberries, pineapple, peaches, oranges, apples, raisins, broccoli, cauliflower, and so much more in no particular combination. Low fat yogurt also makes a great snack. We love getting vanilla yogurt and adding some kind of granola or even bran flake cereal.
Don't argue with her, just let the healthy snacks be available for everyone to consume at snack time and see what happens. Just know at some point she is going to choose to eat the junk but you would have laid down a healthy foundation that she will return to or at least find balance in what she decides to snack on.