Does she not realise that planes are not restaurants with a chef where things can be made to order? Meals are precooked, bought on board in chilled trolleys and then heated up. There are no fridges as such.
Even though an airlines only actual obligation to you when you buy a ticket is transport you safely from a to b, they do offer an array of 'special' meals, including vegetarian, vegan, kosher, diabetic, gluten free, to name but a few. Once an airline starts venturing into the realms of medical meals, apart from the practicalities of getting one 'extra special' meal on to one of maybe hundreds of flights that day, they leave themselves open to liability if the passenger later becomes sick.
Imogen herself has said that her stomach condition is very rare and complex so you would think, in order to not spoil the beginning of her hols she would just eat before and then take some snacks (which is all we ever see her eat anyway) that she knows for sure her stomach can tolerate .... but God forbid one of these influencers should put their hand in their own pocket for once in their lives.