I don't have experience with a c-section, but breast feeding will help her burn more calories. Otherwise, she needs to do all the same things that anyone else that wants to lose weight needs to do: eat at a caloric deficit. Perhaps it will take her a little longer than someone else, but it will happen. The important thing is not to get frustrated and look for a quick fix. For me, losing weight has become easier since I started eating less carbs. Instead of having oatmeal for breakfast, I have eggs. Instead of a burrito for lunch, I have a salad with chicken. Instead of pasta for dinner, I'll have a salad with fish. For a snack, I'll have a Greek yogurt with blueberries. I don't consume any sugar (except for 1 or 2 fruits a day) or anything with flour.