It's not totally impossible to do this diet while being a veggie, however her food choices are going to be very limited and probably quite boring.

She is allowed any and all low carb veggies, cauliflower, spinach, brocolli etc, tofu is good as well. Does she eat eggs, fish and shell fish? Or is she a true vegan? If a true vegan she may get fed up with the menu after about 3 weeks.