Hmm I'm pretty sure my kids were on at least 3 or 4 bottles a day of formula at that age - around 250ml a pop.

Can you try and reduce her solids? Or give her the formula before the solids (sorry if this is what you already do, I'm just thinking out loud..) or... gee I dunno!!! I've never had this problem - has it been going on a long time? I remember DD1 doing this for about a week at a time when she was cutting teeth..