We are told here that they need the fat in homogenized until two yrs for brain development, it hasn't got anything to do with height/weight. I have heard that constipation can be caused by cow's milk regardless if fat content if there is a digestion issue, so you could try switching to a dairy free alternative. with the cow's milk. Also, a diet that is high fat / low fibre can cause it, so you could try adding more fruit to her diet (not bananas, as they can trigger) and offering more water.