Hello, I can understand your worries. My son is skinny and a picky eater too. I finally gave up worrying about his weight, since most of his little playmates are overweight. One thing our doctor told us was to slow down on the milk, because milk fills them up too fast causing a slight weight gaining problem. (They still need milk, but one shouldn't go over board on it.) I do try to make sure he does eat something though. Everyday, I give him a multi-vitamin, 8 oz. of strawberry flavored whole milk, (I worry more about him not drinking milk, than the sugar content.) have him eat something for breakfast, (frozen pancakes, waffles, Goldfish, crackers, croutons, cereal...whatever I can get down him.)...for lunch I pack him a protein, (sausage, pepperoni, Bagel Bites, Pizza Blasts, turkey bacon-he doesn't like the "real" stuff, turkey luncheon meat) a fruit, string cheese, juice, and chips. (He won't eat bread at lunch-time.)...super is rice or pasta, (He doesn't like potatoes, because they're mushy.)raw peppers or cucumbers or broccoli, (The only vegies he'll eat!)and broiled lean meat or broiled salmon and soda or Coolaid...Night snack is yogurt or ice-cream, (The dirty bugger discovered my fat-free ice-cream, which really irritates me since I want him to eat the whole milk ice-cream!) and peanuts or popcorn.
You might want to talk with you're daughter to find out why she doesn't like certian foods to help you work around her. My son doesn't like mushy stuff, messy stuff, or fat. (He spits out the fat in the meats.) That means that everything has to be crunchy and have no sauce. He'll only eat his meat or fish broiled. Children can be funny when it comes to the texture and smell of their food. Hope this helps.