Oh your poor DD. My heart goes out to that child sitting alone in the park, eating her feelings.
her GP has said that she isn't illegible for weight loss surgery as she doesn't have diabetes
Not quite the full picture. Basically it depends on her BMI.
If her BMI is over 40, she can be referred to start what's called "the pathway" to bariatrics immediately. First phase of this is usually being sent to a dietician or weight loss group by the GP. There will then be several more steps before a final decision is made whether to operate. Basically she has to try to make the effort first.
If her BMI is between 35 and 40, she would be eligible to start the pathway if she has any other condition which weight loss would improve. This could be something like diabetes, high blood pressure, joint pain, PCOS.
My BMI was 51 when I was referred, and I'd already been down the dietician route when my BMI was about 40. Gastric bypass changed my life. It is really hard - the hardest thing physically I've ever done. I spent the first 6 months vomiting at least once a day as I slowly tried to add foods back to my diet. But I've got my life back. I lost 50% of my body weight. 3.5 years out I am still restricted in what I can eat but can generally manage a full adult portion in a restaurant as long as I stick to the right foods.
PM me if you want to talk further about bypass.