I am very aware of the many possible medical reasons for MS or, for that matter, any other physical ailment. Most of us breathe polluted air, drink questionable water and eat foods loaded with pesticides and preservatives. It is no wonder that our bodies cave in under this onslaught. In your friend's case, however, the emotional load she carries is likely to drag heavily on her immune system. Healthy immune systems can withstand a lot.
Unhealthy ones lead to serious disease.
With the understanding that I'm not a physician and don't know the first thing about medicine, let me suggest what I would do if this lady and I were working together. First, I would assume that the primary cause of her MS is her emotional burden. I could be wrong, of course, but that's where I would come from. Along the way she is likely to lead me into deeper waters as she begins to recall even more memories. Above all, however, I would persist.