Regardless of whether a child needs more calories, it's helpful to make sure that the food the child is eating is made from good ingredients and real foods. For example: tacos. Many people make them at home by starting with real meat or chicken, and then they dump taco seasoning on it from a packet. The ingredients contain several different kinds of sugars. A homemade taco seasoning that tastes nearly identical to the packaged stuff but is only made with real spices is easy to make, and recipes are available online. Same thing for taco sauce: skip the bottled stuff and make a fresh salsa (chopped tomatoes, onions, cilantro, whatever you like) and you'll eliminate all those sugars and junk processed ingredients.
My dd loves Panko chicken nuggets: just chicken breast meat cut into bite-sized pieces, dipped in milk, then Panko bread crumbs seasoned with a little salt and cumin, and browned briefly in a skillet. Pop them, once they're quickly golden brown, into the oven for about 15 minutes and they're delicious.
Wraps are great on-the-go and can be filled with beans, chicken and healthy seasonings. A sectioned plastic lunch box with chunks of real cheese, natural deli meats without nitrates and nitrites, raisins and nuts can be a great snack. Make breakfast cookies (lots of recipes online) that are healthy, filling, bite-size chunks of oats, fruits, nuts. You can look up recipes that specifically are egg-free. Drain-free packets of tuna and some whole grain crackers make a quick easy snack. Learn to make your own ranch dressing (lots of "copy cat" recipes online, so you can control the sugars and artificial ingredients), and serve ranch dip with baby carrots.
Keep foods small. Have bowls of grapes and strawberries available, and things like Baby Bel cheeses, available at hand in the fridge, washed and ready to grab.
Read labels, and educate yourself about the grocery store foods and fast food ingredients. Choose real foods that don't contain sugars. Learn all the words for sugar (dextrose, erythritol, sorbitol, Splenda, anything that ends in -ose, for example), and eliminate those and things that say "sugar free" (they usually contain artificial sugars. Learn to use raw natural honey and pure maple syrup for sweetening things when necessary. Don't use processed sweeteners like agave nectar and stevia (the real stevia plant is ok, but anything on the grocery store shelf is likely highly chemically processed).
Don't use things from boxes and mixes and packets, because they're packed with fillers, and your daughter will miss out on the real foods.