Where In Europe Did Susan Move To?
Didn't she move to Sweden before she moved to Australia?
Here's a thought. I thought I remember seeing some sort of correspondence from the World Health Organization (or something similar) to the Hanso Foundation on his website. In the letter, it spoke about some sort of disease or experiment gone wrong in Africa.
What if Susan got sick because she was connected to Hanso operations. Individuals whom were exposed to this sickness in Africa and came in contact with Susan. Brian's office could possibly represent Hanso.
Maybe that is why she took Walt with her.