@Notesha I agree somewhat. I can see the possibility of the administration not notifying everyone (huge hassle, and school-cafeterias are not always directly affiliated to the schools) and rely on her doing whatever she regularly does to communicate outside school, but it still seems a bit odd as them doing their job and getting the word out is the more likely option.
I don't agree that they wouldn't believe her tho, aside from the fact that few ppl would be carrying a slate everywhere, there is also the fact that fewer still would pretend to be mute.
That they shouted at her to stop drawing is pretty stupid imo. That is the most unbelievable part. There was no queue (a bit weird) so there was no reason to get upset, and even if there were, it should be pretty obvious she weren't drawing but writing (which would normally make people jump to the assumption that she has a sore throat and can't talk, or trying to figure out what to eat by listing the options she want and apply process of elimination, so they would be patient).
And if she
were drawing (or writing a story) in the middle of the queue, there was probably a decent reason to do so. And if not, probably still more efficient to let her do what she is doing real quickly, instead of interrupting and risking a time-consuming confrontation.