Perhaps your cousin should consider the Schwarzbien Principle diet instead of Atkins. It is a healing diet that nourishes then heals and reduces the 'pollution " we subject ourselves too-ie the frankenfoods.
It she has been diet rotating before trying low carb IMHO it is possible that the protein is being used to rebuild(not bulkup but heal) muscles. Stick to a more whole food ,dark leafy veg,roasts not lunch meat,add some fiber and keep trying.