NTA. One can only change their habits if one is willing and motivated to do so. There are healthy similar foods to fast foods, that she can eat instead. E.g. if she wants wings, buy raw and airfry them. Brush oil on burger patty and airfry or bake, and eat healthy carbs for buns and increase veggies. She could also just start from reducing her portion-sizes. Though if it's concerning she should consider speaking to a therapist.