I suffer from a migraine variant that sounds very similar to the one you are describing that your sister is suffering from. It is a not a common migraine or even what people think of when you explain you are suffering from a migraine condition. My first experience with mine came while I was driving but my pain began with a feeling as if someone had stabbed a knife in my neck. Pain spread down my left arm and my right leg began to go numb, followed by my left side of my face. My left side of my tounge also went numb. Feeling came back somewhat but only as tingling and pins and needle-like. I thought I was either having a stoke or a heart attack. I spent several days in the hospital that yielded nothing. I later went though three doctors. The third actually admitted he had no idea what was wrong and referred me to a neurologist. After months of thinking I was just crazy, my fourth doctor diagnosed me with a migraine variant. Below is a site that explains the different types. I hope this will help you and your sister.

http://www.relieve-migraine-headache.com/migraine-variant.html

A little side note: If for any reason, you are uncomfortable with the doctor's analysis of your sister's condition. Never be afraid to get another opinion from another doctor. Remember that they call them "Practicing Medicine" for a reason. No one is right 100% of the time.

If I had not gone through my four doctors, I would still be wondering what was wrong with me.

Good Luck and bless both you and your sister.