I feel your pain but in my case it was my own daughter.....so stressful. i would suggest giving her just a small portion of what you're serving. like literally 1 pea, 1 carrot etc. too much on the plate can make the child feel overwhelmed and stressed. I would also talk to the parents and let them know that you're offering healthy balanced meals and you encourage her to eat but cannot force her.
I have in the past implemented a "no thank you bite" if they want more bread then they need to have at least a lick of all other foods. best of luck!!!