Oh my word, I know exactly how you feel. I have a little one who started a month ago, and she will go the entire day without eating!
It stressed me out at first, and I still feel awful at the end of the day when Mom picks her up and I have to tell her that she didn't eat at all, but I can not sit there with her for an hour while she refuses to touch anything, and I am not a short order cook who will make something different for her. She doesn't care if she doesn't get a dessert (usually an arrowroot, or fruit cup), and she doesn't care that the other kids get to go play once they're finished.
I decided to stop stressing over this, continue to offer her the healthy foods we eat and she can leave the table when the last child finishes up! If it's not on her extremely short list of edible foods, she will not touch it and i'm not about to get my panties in a twist over a stubborn 3 yrs old!