Maybe this is a bad idea, but what about a fitbit?
I've had mine for 2 weeks and I've lost 10lbs already. I am 5ft 9 and 2-3 stone overweight. I am finding it so helpful to log my meals and activity. I am an emotional eater. I get anxious if I feel hungry. I have been loosely following the blood sugar diet and it has been great.
Today, for example, I have had,
2 boiled eggs for breakfast
Greek yoghurt with seeds and berries
Handful of almonds
Pork and pineapple kebabs with mixed grains and salad
2 squares of sea salt chocolate
Tea and coffee and a diet Pepsi.
That's about 1400 calories.
All I've done is try to meet my targets every day, which involves climbing 20 flights of stairs, taking 10,000 steps, 60 minutes of activity and 8 hours sleep. It also reminds me to move every hour. I have it set to lose 2lbs a week.
Maybe it would help your daughter to think about the choices she is making but without sticking to a diet or strict regime. She will see that she can have a treat but she will need to walk a bit longer for example, or she will see how much sugar she is having in her drinks or snacks.
Maybe by being more aware, she will find it easier to take control.