The OP's daughter may not have eaten since breakfast.
My own daughter is autistic and would've been extremely upset if she missed lunch aged 10 years.
We had breakfast at 7.30 am before school. My daughter would be ravenous at break time (10.30 am) and would have a biscuit in her school bag for a snack. (Other children would typically have bags of crisps.). When school introduced healthy eating in the mid nineties biscuits/crisps were banned. Being autistic, she was a strictly routine character and couldn't understand why she couldn't continue to take her usual biscuit. This caused quite a bit of upset. She wouldn't eat fruit/raw carrot as she had food texture issues.
That meant she had no snack option and would become hysterical at break times and I would get a phone call informing me that 'Your daughter is hysterical, come and pick her up. '
We eventually arranged for her to stay in at break so she could be supervised eating her biscuit away from other children and go to break afterwards. (Thank goodness for the Ed. psych's support.)
If OP's daughter has only had a small (healthy) snack since breakfast, I would imagine she would be terribly upset to miss lunch as well.
I once had to ring a parent to ask if I could give my lunch to their child after I spotted that the sandwich they were about to put in their mouth was mouldy. There were no school dinners left as an option.
The school should have made sure OPs daughter had something to eat, autism or not.
When parents were late picking up their children (after school) I would have them in my class whilst I was marking work and share whatever I had to eat with them (usually Cheerios) because I know children can also be hungry straight after school.
If a child comes into school having forgotten their packed lunch and parents can't deliver it before lunchtime they have a school dinner or a member of staff will provide a packed lunch for the child.
Being late to pick up children from school/phone having no charge happens. It's not intentional. Who can hold up their hand and say they've never made mistakes?
Schools should recognise that the blood sugar dips, due to long periods of time between eating, can cause certain symptoms which can affect how a child behaves and performs.
My granddaughter's school have acknowledged this and children now have the opportunity for a mid afternoon snack.
Every single potential circumstance cannot be anticipated - cut the OP some slack.
I would let the school know that they neglected a child on that particular day.
My daughter is now an adult and is still badly affected by blood sugar dips - she gets 'the shakes', gets anxious, can become very short tempered and tearful and this state often brings on migraines. Some people simply just feel hungry.
Going without food for long periods does have consequences. PP saying that 'she won't starve' need to learn to have some respect.
The OP said her daughter was upset as a result of having no lunch - we don't know the extent of that 'upset'.
Don't judge.