I 've been at the same position when my daughter was around that age (she's nine now). What we were doing at that time, was that she was having throughout the day two different combinations of milk. It was a mix of regular milk and formula with different ratios of each. Further more, she was having a concentrated protein mix (PKU1 of Milupa) only in one combination. I found out after 3-4 days of refusing to eat and lots of crying, that she preferred better the milk containing PKU1, which is now having every time. I think at this age they start to have a more developed taste. Maybe this is the case with you, she prefers the one combination to another. Try to figure out if she's having one meal and skips the other.I hope this helps.