Unless she is showing signs of deficiency, usually exclusively breastfed babies do not need supplemental iron. Breastmilk contains small amounts of iron but it is very bio available. Supplemental iron will block iron in the breastmilk. Rice cereal is a poor first food. It is processed and devoid of nutrients (mainly a filler) and the iron is added. Better to introduce fruits and veggies and organic meat if there is an iron problem. It is true that in the second half of the baby's first year that iron stores begin to diminish and that the breastmilk has small amounts. I just seems to think that if nature wanted breastmilk to be high in iron it would be that way. All of the charts etc are not based on exclusively breastfed babies.
I have seen lots of exclusively breastfed children be diagnosed as low in iron. This normally works itself out as they begin to eat more food in the 2nd year. I think truly anemic babies are pretty rare.
My suggestion would be to find a pediatrician who knows more about breastfeeding and breastfed children and or get a second opinion on the iron. Did they do bloodwork?