I use S26 but we had the same problem when I changed her to Step 2 formula, she was badly constipated for a couple of weeks and i decided to change back to Step 1 because nothing else was working. She doesn't eat a whole lot of solids, yoghurt/fruit in the morning, a piece of bread & vegemite or a cruskit for lunch and vegies for dinner. I just put some leftover spag bol in the freezer which I pureed up a little bit for her and she doesn't seem to keen on it yet. Some green vegies are supposed to have a fair bit of iron so maybe offer her some for dinner if you feel she isn't getting enough out of her food. I would say she would be fine though, i don't think there is a huge difference in the amount of iron between formulas