I had this with my daughter to the point that when we did get her to eat she would just vomit. It was really difficult it all started when she had Rota Virus when she was a baby, she had started on solid foods and we had to stop them and put her back on milk, watered down.
She was so underweight and wasn't a big baby to begin with 5Ib at birth and she was born on her due date so not premature or anything. When I look back at photos I wonder how her head stayed on her neck it was that thin.
Anyway after making all the usual fuss to get her to eat, ignoring meal times, passing her around relatives when it was meal times so that we were not seen as bad parents in my daughters eyes.
She started school, took her lunch in a bag as the other children did only she brought hers home again untouched. She made some friends and was invited for tea and she would eat something, not much but something, her friends parents were aware of her food phobia, so never pushed it, she saw her friend eat so she joined in. Then she came home and would eat something from our plates not much we ignored it, then she became involved in making the tea through her own choice and started to insist that things were put on a plate for her and she would eat. She had days still where she would not eat and we never pushed it, believing that she would do it when she wanted to.
We gave her multi vitamins daily. She saw loads of doctors who didn't know how to help, she was never given a label or a diagnosis as to why she couldn't, wouldn't eat. She was prescribed ensure to make sure that she was getting some nutrition. I believe that it started from the rota virus.
She is now 14 years old of fantastic height and weight, she still goes through spells of not eating but makes up for it on the days that she does eat.
I know that this is not going to help but I wanted to share with you how we dealt with our daughters problem.
Good luck.