I tell parents before they even start that drop off needs to be short and sweet.
As for the food, She will not starve herself, just keep trying and she will either eat or not, not your job to force her to eat. Talk to the parents about habits at home. maybe she is used to grazing and not used to sitting at the table. I see that a lot with new kids. Also suggest that they visit a dentist with her and suggest that maybe her teeth hurt to chew food. If they are rotting then that is very possible. If they don't have coverage i know many communities have free dental care for families without.
Hang in there i am sure it will get better soon!