The atkins diet is not the same as the atkins diet
So son't worry about that. She'll gain weight and get all the nutrients she needs from it and will also probably take in a little less junk from processed flour products!
Atkins banishes and restricts carbohydrate foods rather than just those containing gluten, whereas on a Coeliac diet she will be allowed as much as she likes form the following starchy foods (as long as not prepared with gluten containing ones!)...
Potatoes, rice, yams, cassava/tapioca, corn, polenta (cornmeal), quinoa, millet, amaranth, arrowroot, and other less common grains and starches.
Some people will tolerate some oats but many prefer to avoid them as a matter of course.
She will also get carbs from fruits, vegetables and pulses/lentils.
All meats and fish in their natural state are free of gluten, as are eggs, dairy foods (check label on processed ones), and nuts and seeds.
So a typical day could be:
Rice cereal such as krispies/cornflakes/millet flake porridge/ with banana and milk
Apple and some cheese/yoghurt/milk/chocolate/ricecakes/dried fruit/crisps for a snack
Gluten free bread/ rice cakes with hummus and veggies for dipping/soup/bean salad/sweetcorn fritters/polenta pie
Any meat or fish with mash/rice/baked spuds etc and veg.
HTH!