There are loads of things you can cook for her - rice (esp brown rice which is higher in fibre, which can also be lacking in a gf diet), potatoes, corn and quinoa are all naturally gluten-free. There are also plenty of gluten-free pastas available.

All fresh fruit and veg are gluten-free, as is all plain meat.

I was diagnosed Coeliac 27 years ago at the age of 14, and pretty much everything I cook is gf (esp since my 6 year old son was diagnosed a couple of months ago). The healthy eating guidelines are pretty much the same as for anyone. Have sensibly-sized portions, eat plenty of fruit and veg (at least 5 portions daily) and don’t fill up on sugary and fatty snacks.

If your daughter has only recently been diagnosed, you may well find that as she adjusts to a gluten-free diet her weight falls off without too much effort. It isn’t uncommon for patients to be overweight at diagnosis. (The body cannot absorb all the nutrients it needs from a diet containing gluten, and so the patient feels hungry all the time, and so overeats, and puts on too much weight - once gluten is removed and the gut has had a chance to heal, the appetite has a chance to return to normal.)

How old is your daughter? If she is old enough it is a good idea to get her as involved as possible in choices about her food - she will probably have to cook for herself when she leaves home, and at the very least needs to know what to look for on labels. The more involved she is, the more in control of the situation she will be.

I hope this is some help.