Hi Kathy,
I'm sorry to hear that your sister is dealing with moyamoya. I can only tell you my story and hope that it helps her to seek the opinion from a moyamoya specialist.
Late last Fall, I had surgeries on both sides with Dr. Gary Steinberg at Stanford Hospital. My neurologist also was unwilling to give a diagnosis of moyamoya. He told me he thought I had atherosclerosis, due to many years of high blood pressure and more recently slightly high cholesterol - both of which were well under control. He prescribed aspirin and Plavix (clopidogrel), then told me that when I had my next stroke to go immediately to the ER. There was never a question of my having another stroke, only when it would occur and how devastating it would be. Fortunately, I found the words "possible moyamoya" mentioned several times in my medical records. I did research at the University of Washington Medical Library where I continuouly encounterd Dr. Steinberg's name in connection with adult moyamoya and found this website.  I called the Stanford Moyamoya clinic and overnighted my test results and CDs containing the MRI/MRA and angiogram to his office on Friday. Monday evenings Dr. Steinberg and his team review all records received the previous week. His nurse, Teresa Bell-Stevens called me that Monday immediately after the coference and told me of Dr. Steinberg's opinion and recommendation. My surgeries were scheduled and I was in surgery within a month. They take this disease and the immediate risk of stroke very seriously and act accordingly.
I've asked myself repeatedly why my neurologist was so reluctant to consider surgery - I can only conclude that it was ingnorance.
You can contact Dr.Steinberg's office and ask for his opinion regarding your sister's ANA and other test results. He charges nothing for this service.
Best wishes to your sister and your family and Happy Easter to you all.
Kim