Hi,
I am 29 and was diagnosed with M.S when I was 21. The M.S website is brilliant and I'm sure will answer most, if not all of your questions.
http://www.mssociety.org.uk/
There is also a section on there for family & friends as well, which my family found very useful
Usually M.S will not be diagnosed in the 1st year of symptoms, as it can easily have alot of the same symptoms as a lot of other illness's/disesases (I hate that word).
I am sure that they will carry out many more tests, and may turn out to be something totally different...
I wish you and your bfriend's sister all the best and I'll be happy to answer any questions I can
S xx