|(Unless you want to give a crack at why she starves herself to the point that she loses weight-- when she's already at the zero percentile. Or why she'll eat a food one day from one person, then refuse it from me the next day at home.)|
Our son is sensory adverse orally, so we have a lot of foods that he won't try or refuses after just one bite. Fortunately, he likes smoothies and I add all kinds of supplements to them: flax seed oil, magnesium, probiotics, B-vitamin supplements, calcium, Vit. C, protein powders, coconut oil, and fruit. He loves them. I also use protein powders in pancakes, waffles, cakes, muffins, etc. He loves fruits and vegetables, but like your daughter, it changes from one day to the next. He'll eat two apples in one day, then none for a week.
Same with asparagus, spinach, pork, chicken, beef, etc. He'll eat a huge portion but refuse it the next time it is served. I figure it all balances out.
I add calories by adding oil to the smoothies and extra oil to my baking. Ds likes peanut butter (before age two I'd use almond butter, less allergenic). It has a lot of calories. Avacados do too. Getting enough calories is an on-going awareness of mine because our son is so physical and active. But, sometimes he'll eat little for several days and then eat adult portions of an amazing quantity of food. We are more grazers than big meal eaters though ususally.