What Causes Concussion?

My daughter is 16. Fainted in a mall, ambulance came. Bp 80/57 at the time. History includes concussion in late July and broken sesamoid bone in foot. Mild headache for 3 days. Went to Er said maybe a virus. She had visual disturbances for 30 min , dizziness and nausea. Otherwise healthy individual, playing soccer for yrs before broken bone. History of a great Aunt with stroke at 26 , diabetes in grandfather. No fever, actually, 96.5 at hospital. She seems fine now. Has had periods of dizziness before but no fainting with it. Had eaten breakfast 4 hours prior. No history of drug use, not pregnant and no alcohol. Seemed neurologically fine on initial exam. Grandma feels blood work should be done for thyroid and diabetes and mri because of concussion in July. She did not pass out from that head bump but was incoherant at that time and unable to move her limbs. She took time off from sports mild headache and no further symptoms.