My friend has been feeling like she was ready to faint for the last 11hrs and said that it has been happening on and off for months, what should we do

See a physician: There are many reasons as to why a young person might experience lightheadedness, which depend on the circumstances during which the symptoms occur; i.e with sudden changes in position (orthostasis), palpitations (arrhythmias), dehydration, pain and others. Given your friend's symptoms have been ongoing for a while I suggest seeing a physician for evaluation. In the meantime, keep well hydrated.