If your child is in either years 1 or 2. or has qualified for free school meals, the school is breaking the law:
https://www.gov.uk/government/news/free-school-lunch-for-every-child-in-infant-school
and
https://www.gov.uk/guidance/univers...meals-guide-for-schools-and-local-authorities
While May intends to repeal the UIFSM program, she hasn't yet. This means that - assuming your child is in either year 1 or 2 OR is "disadvantaged" (i.e. qualifies for free school meals) the school is required to provide her with a hot, nutritious lunch.
The term "universal" has been legally demonstrated to mean "every child according to their need" which is why schools must now offer halal and vegetarian options. Your child, according to her need, requires a low-carb diet. If the school is failing / refusing to provide this, they are failing to provide "universal" school lunches. And, therefore, they are both breaking the law by failing to provide a child with a hot school lunch, but also they are doing it because of her diabetes - which is discriminatory.
They are also breaking the Equality Act 2010 which provides further protections for people with disabilities (non age-specific) and, I suspect, a good solicitor will find them in violation of both the new Code of Practice for schools as well as The Children and Families Act 2015 which adds further, specific protections for children with disabilities.
Contact your local SENDIASS (Independent education, information and advice service) for immediate support, and The Law Society (
https://www.lawsociety.org.uk/) to find a good SEN Law solicitor who can take this on. Also, copy your Local Education Authority (LEA), particularly whoever runs / commissions their SEND department (your SENDIASS will know who this is) to every letter and email and invite them to every meeting. They probably won't respond, but they'll get seriously irritated and might be moved to intervene, and it'll save time if this judicial review because they'll already be well-informed of your complaint.
Plus, even if your school is an academy (instead of a maintained school that gets its funding directly from the LEA), they have to provide whatever they have been contracted to by your LEA - that is to say, they have been commissioned to offer, at the very least, a service that is non-discriminatory and follows all legal guidelines. The LEA might well force the school to take appropriate action if this is brought to the right person's attention.
*A note on separating good solicitors from bad ones: A bad solicitor will tell you that education cases no longer quality for Legal Aid in England and Wales. A good one won't.
Hope that helps!
Sock x