With both my daughter and my grandson, I could observe a real progression between ages 2 and 5 in their ability to sit and focus on eating. There's also the extremely common tendency of toddlers to suddenly develop a very uneven appetite that almost disappears for days on end, and start eating fewer foods and much LESS than parents think is possible to survive on. That appetite will become more consistent again around 5 or 6 for most kids.
Research suggests that the sudden dislike for many foods is possibly nature's way of protecting kids from eating dangerous things in their environment. Foods that have not been a regular part of their menu by the age of 15-20 months are not likely to be attractive to them when that difficult stage hits. Even some foods that they formerly liked may become unappealing during this time. It's not that those kids are trying to make life difficult for mom, they really do not like certain flavors and textures.
There are also studies showing that if allowed to graze and choose from a broad selection of healthy foods, kids will usually pick a variety, in the amounts needed, to meet healthy dietary requirements. The exception might be kids who have acquired a taste for junky, greasy, sweet or artificially flavored foods in their first year and a half. Modern processed foods are designed to trigger pleasure responses in the brain that will keep customers coming back for more, and this can throw off the natural desire for good, nutritious foods.
Imagine if you were required to eat foods that disgust or alarm you every day, or were urged to eat more than you are hungry for. It would make mealtimes a trial rather than a pleasure, and could drive a wedge between you and those trying to feed you. In fact, eating disorders later in life can often be traced to control issues over meals earlier in life.
Your daughter will probably do much better if you don't think in terms of battles, winning, and losing. I understand the inconvenience of preparing special foods to coax a reluctant eater after cooking a full dinner. But if you were to make a list of healthy foods to keep on hand that could be served cold or quickly warmed that your daughter does like, she should stay well-nourished, happy, and emotionally healthy.
You'll find that even if she can't endure sitting through a whole meal for the next year or so, she will gradually improve if it's not a big fight every day. My grandson, now 6, is a fine meal companion with a good appetite most days. He likes a broad variety of foods, and eats his vegetables happily. That wasn't the case at all two or three years ago, but his parents kept encouraging him sit with the family as long as he could do so without too much stress, try a bite or two of the prepared meal or new foods, and eat as much as he was hungry for.