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
well if he has his doubts and if she thinks she can automatically get ILR in 18 months or whatever,she's wrong, as he's still holding all the cards and it's up to him whether she can stay here or not