Yes, as long as the breast feeding mother doesn't have any specific health problems or needs to be monitored. Any gestational diabetes? Any food intolerances?
I would really recommend she also go as organic (fruits and vegetables) as possible. Everything she eats will also go to the baby. Stay with wild fish and organic chicken. I just posted an excellent research study done by Consumer Reports on Facebook, I would encourage she look at that report for fruits and vegetable that are important to eat organic and which ones are fine grown conventionally.