Never having had a kid yet (i'm 24) I went to go ask my mother this one. She said she is allergic to iron, but only orally - when she was pregnant with me, she had the same problem with the prenatals... when she talked to the doctor, he took her off them and told her to take a children's vitamin every day. When she had chemo for cancer, she had to have the iron by IV for the same reason. She's also a nurse, and said she might get the doctor to run some blood tests to check various levels of things, but its probably an iron allergy, or maybe both since you said she's sensitive to other metals. Hope she figures out what's causing the problem for sure.