A.R.
Hi L.,
First of all, I would start (like other moms said H.) with not buying junk food, and not cooking with too much fat. Basically, no french fries, no chip potatoes, no ice cream of any kind, no cookies, no sugars, and so on.
Portions meals are VERY important together with exercise. She should be eating 5 or 6 balanced meals a day. It sounds a lot for you I guess, but I am talking about SMALL portions. For instance, the size of a piece of chicken breast (no other part of the chicken, too fattening) would be the size of your palm, a cup of salad with no other dressing than olive oil, pinch of salt and may be some lemon o vinegar..This is just an example. No juices at all unless they are from real fruit made at home. Portions are everything! If she is hungry and craves for sugars, smoothies are the best. I usually get frozen fruits, I thawed them and I mix them with plain yoghurt. Nuts are good for snacking too..but....just a handful daily.
I have learned all of this by myself, and I lose weight in that way after every pregnancy. Do not starve her, that would be worst. Get 1% milk for her no whole or skim milk if she likes it. Lots of fruits, mix them!
Anyway I would take her to the doctor so she/he can take a look at her and give you more professional input about it.
Make a lifestyle of it, and she will be OK. At the beginning is very hard to change habits..very hard, It happened to me, but when I could put my old jeans on again...it felt sooooooooooooooo good!!!!
Start with small changes (no ice cream twice a week..) watch PORTIONS!! Have your daughter do some exercise, whatever she likes, walking, running, jumping the rope, gardening..No too much TV. Do you have a dog? take a walk with her and the dog...Encourage her to MOVE...and say nice things to her when she is doing good and eating well.
I hope this helps you. I know it is not easy, but I am sure that it will lasts than going on a diet.
REMEMBER: Do not make this thing look like a diet, it is not...She can eat healthy balanced foods in the right portions. Balanced? (watch that her plate has many colors: greens, yellows, red, browns...) portions??? SMALLS....
Good Luck!!
Alejandra