Exercise won't make much difference in the weight. It might be good for health, mood but not for big changes on the scale.
This said, when stuck in the lockdown, the amount of time, one diverts towards the kitchen in ridiculous.
I might go against the crowd here and tell you to enrol her in revamping your kitchen arguing that both have put on weight, blame it on the lockdown, not her, and sort your fridge. Sauces, processed cheese (anything square) , sugary yogurt if any, drinks and so on.
It is not a diet, be clear, it is a change of life style for the all family and forever. You can talk about weight without being cruel. I found that here in Australia (I am French) there is a taboo about talking about weight .
When she was a baby , you taught her to walk and talk, when she was a child, you taught her to cross the road safely and ride a bicycle, , as a pre-teen now you teach her how to eat for a healthy body. The next step, you will teach her how to shave/wax her legs, and later how to stay safe with boys at parties, who to accept lift from and so on. Weight is one of many tricky conversation. As long as you don’t blame, hurt or shame, it is part of life. Avoiding that conversation might be worse. I don’t know. It might be cultural. In France, we talk but mainly we lead by example and eat a lot less industrial food.
Most days, we have a piece of meat/ fish /eggs / tofu (for me, the only vegan in the family) with a couple of veggies. Avoid fried food from chips to fish or limit them to once a week. Of course , we have rich dishes, but the average weekday dinner is quite simple.
Maybe reconsider the way you cook and eat in the house as a family. Write down the average meals you cook and how you cook it and check them on cronometer.com to a analyse their nutritional value.
Try to cook your meats, fish without sauces or jars, but use fresh herbs, rosemary, extra virgin olive oil, cracked pepper.
Try new dishes and new veggies, aim at 10 different veggies in a week - sounds a lot, but it is less than 2/day. A cucumber and tomatoes salad with some tuna for lunch, brown rice with roasted pumpkin for dinner, a steak with a butter lettuce, omelette and green beans, sautéd spinach and herb coated chicken breast with thinly cut fennel salad with a squeezed orange juice, grated carrots with parsley and roasted chicken ,
Try one of these example once a day.
It is also about the frequency with which you put something in your mouth. In France, normal people don’t eat in the street while walking or carry food/ snack in bags, we don’t take lunch boxes to parks
You can start by watching some sugar movies or industrial food documentaries together.
Also apply some rules on where to eat. Only eat in the kitchen or dinning table, not in front of tv, bedroom and all together as a family .
Of course, you can still prepare pasta, but avoid white sauces or cream. Prepare an authentic sauce with crushed garlic in a pan with olive oil , to which you add a bottle of passata and leave on low heat for 30 min, add salt , pepper and 4 or 5 basil leaves.
Reconsider the bread loaf if you are buying the typical white and maybe bake your own with a mix of wholemeal and spelt. Industrial bread is so spongy, soft and fake. It is hard to binge on old style bread, a slice will satisfy you.
Do not demonise carbs or anything, but do avoid ultra-processed food, industrial artificial food, anything that has more than 4 or 5 ingredients listed, anything that you can't replicate in you kitchen because it need high pressure or a degree in engineering. Try to avoid refined carb, this yes, so white flour, white rice, and so on.
I have listed general observations and most probably don't apply to you, but maybe there are a couple of ideas you might reflect on.
I don’t know you, your DD or family and don’t want to make hurtful assumption. Good on you for seeing an issue, and wanting to tackle it,