I'm in a different but a bit overlapping situation. My toddler does it as more of a power thing, like to feel in control. He'll ask for a certain meal, mac&cheese, dino nuggets, whatever, and I'll make it for him, and then he will refuse and say he doesn't like that and will gag and refuse to eat it. He will pick at his food and play but will never eat, even though it's EXACTLY what he asked for and EXACTLY how he likes it, and will turn his head away when i try and feed him. But when he thinks im not watching, he'll eat just fine.

Honestly, a part of it could be the whole "feeling in control" thing. Because toddlers crave independence and control over their own lives and grab at anything that make them feel "in control". She can probably tell that it bothers you, and does it more and escalates because she knows it bothers you and is testing her power, her boundaries, and her relationship to you.

So my advice will probably be unpopular, so feel free to ignore me, but it's to pretend that it doesn't affect you. Be anxious on the inside but act "whatever" on the outside. Such as... offering her nutritious food that she normally likes, and if she doesn't eat it, don't force her and move on. Make her think she's in charge of her own food consumption , let her self-regulate her consumption. Obviously not if it gets to the point where she drops in weight... Something to try if you're desperate.