How late is too late?

After nearly two years of doctors not agreeing on what was happening with my mother in law, a second opinion neurologist says that he strongly feels that she has a form of GBS…. however because this has come on very gradually, I think it may be CIDP in any event, what are the options for treatment given the lengthy period of time that a diagnosis was lacking? everything i read about IVIG and plasmapheresis seems to indicate that if it isnt done in the first couple of weeks, it won’t do any good.
we are getting her to a specialist in Dallas as soon as we can but the uncertainty is difficult for all