Final answer:
The best source for the 7-year-old girl's medical history would be her family members or guardians, supplemented by observations from school staff.
Step-by-step explanation:
The BEST source of a patient's history of present illness in the scenario presented, where a 7-year-old girl has had a seizure at school and is now only responsive to painful stimulus, would be the information provided by the family members or guardians, as they are most likely to have knowledge of the child's medical history and recent health changes. Considering that children of this age may not be able to provide a reliable medical history themselves, especially post-seizure, it's crucial to acquire details from those who know the patient's baseline health, previous seizure occurrences, if any, and any relevant medical diagnoses, such as epilepsy. Additional information may be gathered from the school staff or witnesses of the event for an accurate clinical picture, but the primary history should come from family members.