If the chicken sandwich wasn't hot enough, I don't understand why it coukd t have been re-heated
The issue here is that this was an adult sized child whom the mother seemed to be implying that she wouldn't be able to control and for whose actions she couldn't be responsible for.
Even if the DD just injured herself, there is the risk of other passengers being distressed by this (and bringing a claim) and the mother arguing that the airline had caused her DD to act like this by not providing a meal and also bringing a claim.
The whole thing is very unfortunate but I would have thought that once the mother realised she coukdbt pre-book a hotmail, she would have been in contact with the airline to discuss how this could be dealt with. If it could t have been dealt with satisfactorily, it would have been sensible to re-book with one of the other airlines that the mother states always provides the meal as required