I am sorry to say that in very rare cases in can spread to the brain... This something that you may want to discuss with her doctor, and maybe have him consult a nerologist.
This is a very rare form of the Virus and though it is never unheard of it can persent itself in later stages.. You have to understand that is how the virus is spread through the central nervous system and that is at the base of the spine, so it is not uncommon for it to effect any area of the nerves. I am very sorry, but keep in mind it could be many other things also that are causing your sisters behavior... Please keep us posted. best wishes to you and your family through this difficult time..

think possitive.