Hi,
My experience of this is they should be a certain weight before they go on the hungry baby food. I would get her weighed then ask the health visitor. It can also cause constipation. What I did with dd2 is the first bottle of the morning and last thing at night were the hungrier baby formula then the rest of the day was the first formula - told by health visitor and also my friend who is a health visitor. We had no constipation issues. As she is now on solids she only has one hungry baby formula of a night the rest is the first baby milk.
If you do switch to the hungry baby formula when they are established on solids you may need to switch back to the first formula as they can fill up on milk and not want the food. This happened with dd1 and it was only when my health visitor friend was talking about dd2 going on it that I realised that is why she never weaned very well.
Hope it helps.