If she didnt eat the whole day she could have had low blood sugar which CAN cause a siezure (its one of my "triggers") It could be a one off, but get her seen by a dr eeither way
could the child have also had a fever at all if so it could have been caused by the fever which would be classed as a febrile convulsion
was she in the sun the whole day? it could have been sunstroke. just remember though about 5% of people will have one seizure in their lifetime and it doesn't mean that anything is wrong, just go to you GP and see what their opinion is. if it does happen again though, then you need to make an appointment to see a neurologist