I am so sorry about your friend. My daughter was misdiagnosed by Dr's in our area for 10 years resulting in 2 strokes. My sister was dx first and the neurosurgeons in VT. told us they had done this surgery 100's of times. They had not it cost my sister 5 strokes after her 1st side and a massive infection the 2nd time resulting in 2 more surgeries and the removal of part of her skull! My opinion about treatment for this disease is use your judgement and pick drs that are qualified only! Find literature they have written and verify their credentials. If not for this site my daughter would have faced the same possible outcome! but we found Dr. Scott right here thank God and D.J.  Charl

I am deeply sorry for the loss of your friend.  There aren't any words that will make what happened ok. 
You, as well as her family are in my thoughts. 

The sad truth is that there are not enough doctors who have the knowledge and experience to treat this disease and fewer still who will admit that they aren't qualified and help their patients find a doctor who is.  As a result, moyamoya often goes undiagnosed, underdiagnosed or in your friend's case,  mistreated.  It is frightening, frustrating, infuriating and on and on and on...

What we can do is EDUCATE, EDUCATE, EDUCATE.  Tell everyone you know about this disease - it's signs, it's symptoms, and above all, that it can be treated by some wonderfully dedicated, experienced doctors.  Tell your doctors (mine had never even heard of it when I was diagnosed).  Trust your instincts about your own health and treatment.  Always be your own advocate.  Care for and support the patients and families who have been affected by this disease.

Peace to you.