We have 3 family members who are coeliacs. We have had no issue with BA as we always reserve the meal in advance, as anyone with half a brain knows you have to do. For our child who is a coeliac we of course take extra food and snacks to ensure that they can eat throughout as and when they want to. I would assume this is what anyone with special dietary requirements does. Indeed I think you can get extra baggage allowance specifically for this.

She sounds horrifically entitled. I also don't think 9 hours without an actual meal would make anyone throw up, especially given the crew tried to help by providing some GF food for her.