A.D.
Similac makes an organic formula that is widely available (Target, drugstores, grocery stores) and Whole Foods carries several brands if she has one of those stores near where she lives/shops.
I agree with those who say BFing is best, but sometimes it's hard to pump at work. Not everyone has a flexible workplace with a place to pump other than the toilet stall (yuck) or gets more than a half an hour's lunch break. Mom has to eat, too. Tell your sister whatever she decides will be fine for her child. And what a good sister you are to try to help her out. :)