My son has stains on his baby teeth from the multivitamins with iron. I took him to the pediatric dentist to be sure they are just stains, and nothing else. They assured me that they can easily be removed, and even tested on a spot to see that it can be removed. But he was very little then and did not like it :-) They told me they can remove them completely when he is a bit older and will cooperate (around 3).
I noticed that the stains are better now, as he is not on the multivitamins anymore, and I clean his teeth with a brush and it helps to get rid of the stains.
I would take him to a pediatric dentist to make sure they are due to the iron.
Are you giving her the iron supplement using a dropper, or adding it to something she drinks? I think it would be better to give it with a dropper towards the back of her mouth so it does not contact the teeth as much.
You can also wipe her teeth with a wet wash cloth after giving the supplements, and be sure to clean those two precious teeth with a finger cot or a brush regularly :-)