Hello,
To lose weight a careful diet and regular exercise is necessary. Your daughter should eat Eggs, beans, green tea, salads, fruits like pears, papayas, soups like chichken soup, lean meats, tofu, nuts, high fiber cereal, nuts like walnuts, oatmeal, brown rice and multigrain hot cereals.
Regarding foods that she should avoid in order not to gain any weight are fizzy drinks, processed foods, oily and fried foods, Red meat, butter, whole-fat cheese, Margarine (especially stick), cakes, pies, frostings and fried foods (i.e., French fries, fried chicken), hot dogs, cheese, tomato sauce, canned and dried soup, deli meat, frozen pizza, potato and pasta mixes and frozen dinners.
It is very difficult to precisely confirm a diagnosis without examination and investigations and the answer is based on the medical information provided. For exact diagnosis, you are requested to consult your doctor. I sincerely hope that helps. Take care and please do keep me posted on how you are doing.
Low carb diet will help her lose weight. It will also reduce her insulin requirements (so she needs to monitor carefully).
There are many online links (you will need to search as I'm not allowed to post links here) if you google low carb and diabetes management.
For an excellent book look for "diabetes solutions" by Dr. Richard Bernstein. I found that book revolutionised how I think about diabetes and how I manage it for myself (all for the better).