They didn't get any paperwork or input on what she was using while in Guatemala? I'd think they would have informed her that she was drinking whole milk or whatever.
And thier pediatrician is probably no help. As much as they should know better, most will allow/advise as witch so often that you never know what the child is needing.
I don't know how you could advise them if they aren't being receptive. It takes 2 weeks for a childs body to settle into new milk.