Hello sir. Sudden giddiness and blackouts are very common which are related to problems like hypoglycemia which is very rarely picked up on investigations on the time of complaints.  Also dehydration,  arrythemias,  migraine,  etc.  I would suggest you to look for any of this issue when it happens further.  Do an EKG to rule out any cardiac issues. Make sure shes always well dehydrated. Thank you