One other possibility - is your child being bullied at lunch time? Did someone "steal" or "make fun" of her sandwiches and that is why she wanted the dinners? Just wondering ...
Did you say this is only school meals or home also?
There is anxiety with some children at school cafeterias. Mostly children that don't like noise- and believe me I worked almost every day in the school cafeteria as a monitor for 20 years- there is nothing to do about the noise level but fuss and fuss and the children DO get quiet/ for about 2 minutes/ then it is loud again..... Our principal even finally gave up and just said let them go to the playground as soon as they are finished eating.
You may try going up there and seeing about the noise level since you mentioned she is sensitive to loud voices.
The only intervention we had for children like this was to let them eat outside the lunch room perhaps with the counselor and a friend- maybe to make them feel as if they are not in trouble.
I am wondering if they rush the childrento eat, at school lunch, and if she likes to take her time eating this would cause her to feel anxious, so speak to her and give her the choice of sandwiches again, ask her if they do hurry the children to eat, this does happen,You are correct in not feeding into her behavior but perhaps talk to her and find out if she is unhappy about anything and why.