Fostering and SGO

We have been asked to look at going down the SGO route for the little girl we foster and have done for over 4 years now. The information on here seems to be quite old and I was wondering if there is any updated news about finances? We are both retired, my wife was asked, not told, by social services if she would stop work to look after the little one when she came into care in December 2014 as there were some needs, not special needs as such. Obviously now my wife will not get another job but will not get her pension for 5 years and my income is my pensions. We can manage nicely with the fostering allowance but if it was stopped after 2 years it could be different. Our LA only pays the allowance at the moment, we do not get anything else like some LA's give weekly payments as a "holding" payment as such for being with them. Reading on here that a few years ago some people got the allowance until the child reached 18 is this more commonplace these days or not? We would certainly prefer to go down the SGO route.