well all he has to do is not sign her ILR app and apply for FLR instead, stating she has not passed the life in uk test, so she will probably be given a further 2 yrs FLR. it gives them a further 2yrs to see how they get on or dont get on
FLR/ILR won't exist by then, but I guess they will be a similar option...
But if things are going well (or a least look to be going well..) after two years, suggesting a further probationary period might cause a bit of an arguement