Why don't you tell us an example of what she eats over the course of the day and how many times in a day, she will have something.
In France, there is nothing in between meals, for the exception of the 4 pm afternoon snack, even young children will have breakfast and then nothing till 12.30, 4 pm, 7 pm for younger and then nothing after dinner.
I moved to Australia, and here people eat all the time, everywhere, while walking, in cars, in parks, on the beach, eat eat eat., It was very strange for me at first. Mothers carry food in their bags, have snacks in car, .... The habit of snacking is encouraged from very young, with toddlers in prams always with a packet of snack in their hands, baby weaned with puffs and crisps, ....
I have to say that nobody has sandwiches for lunch if you are home. We will have some meat, fish, with raw and cooked vegetables. The second difference is that we only eat sitting at a table, not in bedrooms or lounges.
So where does this leave you. Maybe - if this is the case in your house - state that you want a cleaner house and that nobody eats anywhere but sitting down at dinning table or kitchen bench. Never in front of tv.
Clean your cupboards and put all snacks and processed food out of sight. Crisps, rice cakes, and other ultra processed food should however not be bought again. You are not eliminating them but will give 3 biscuits on a plate at 4 for afternoon snack or a slice of cake, a crepe, for breakfast. Even some chocolate squares in a bread roll. So a child has their little pleasure, no obsession.
I think the biggest difference would come from removing processed food wihich not only cause extremed cravings but will cause an unnatural weight gain. Processed industrial cheeses, spreads, hummus, even the breads, so spongy and artificial. try to go for more natural versions of cheese, breads. Industrial cheese (easy to identify, it is square and with plastic sheets) which your DD has a fondness for is well so artificial it is a combination of fat with a sweet taste. IT is not her fault.
You are scared of history repeating itself but you don't have to. With the lockdowns and being all the time at home, boredom kicks in and of course, a kid will visit the fridge every hour. But if there isn't much in the fridge but fresh food, or in the pantry no processed food, hopefully she will lose the habit.
I recommend for you, not your DD , this book www.amazon.co.uk/gp/product/B06XCPNLCQ/ref=dbs_a_def_rwt_hsch_vapi_tkin_p1_i0?tag=mumsnetforu03-21 about how processed food is affecting the body
It might be difficult to change the habits and meals, but it is a matter of a couple of weeks.