My sister has severe coeliac disease - she was diagnosed over 20 years ago. It is a serious condition, and she does have to be incredibly careful over what she eats. For instance, she cannot share butter with non coeliacs, because if only a few crumbs from normal bread are in the butter dish, it could affect her. And the effect is like major food poisoning. She shakes, vomits, has explosive diarrhoea and is very, very ill. However, it is purely a case of being vigilant and sensible.
For the suggestion that Megan "can only snack on ham and cheese" is a load of old dramatic nonsense. Additionally, all ham and cheese products are not necessarily gluten free and therefore not all brands are safe for coeliacs! There is a plethora of gluten free snacks - all fruit, all vegetables, rice cakes and a huge range of gluten free snacks, crisps etc and products are available and actually much safer than ham and cheese!
Alongside this - coeliacs have to be extra vigilant about alcohol as the distillation process can mean that there will be a small amount of gluten in some drinks. If my sister is even remotely unsure about what she's being offered, she will turn it down as she doesn't want to spend the next week in the toilet feeling like her stomach is being turned inside out.
It is a difficult disease to manage - however, not having the correct food does NOT make sufferers throw tantrums.