It is inflammation of the meninges, which filters blood before it goes to the brain (it is also known as the blood-brain barrier, similar in function to the placenta except it's for the delicate brain). When the meninges suffers from insufficient circulation, inflammation increases the pressure to force the cells to accept the blood's nutrients, like putting your finger on the end of a hose to get a stronger flow. That pressure is what causes the pain.

Usually the cell has poor circulation (in a cell it's not really circulation, but rather acceptance of nutrients from the blood) because of something in the blood. If your friend regularly eats onions or garlic or something like that, that could be the cause. Either way, keeping the blood clean will help the meninges to accept blood flow regularly and without inflammation. The first thing is to drink water with minerals (sea salt), and that will immediately improve the blood's acceptance by the cells.

Given that the migraines are persistent, it may take some time for them to go away for good, though the severity should drop incrementally, especially if the person can avoid the offending ingredient(s) or foods. To do the job right and perform a proper clean-up, avoid carbs, sugar, spices and vegetables with intense flavors (like onions and garlic).

This guy can sound a little wacky, but I have found his health advice to be very reliable and effective. https://darkovelcek.wordpress.com/2016/10/19/migraine-fiasco/

Hope it helps!