I think ready brek is fortified with iron and there are some iron rich foods such as green leafy veg, apricots, raisins, beans and red meat but if she's eating a balanced diet iron deficiency shouldn't be a worry.
If you think that vit c might help, what about something like ready brek with raisins for breakfast some days?
Hello, I did some research about iron intake and summarised it here: about iron in children's diets It includes an idea about how much iron children need at different stages of their growth and possible sources. Vitamin C does aid absorption of iron. To support my daughter's iron intake, I give her apricots and other dried fruit sometimes as snacks (although not too often due to potential to harm teeth) and in puddings such as wild apricot fool. We are vegetarian and enjoy a lot of lentils and pulse that are also a good source of iron. This lentil bolagnese tends to go down well with most children so you could give that a shot.