I like how your mind works, that angle could give the series some new life for a chapter or three. And it doesn't even require the cliché of "I can fix him" or at least Sarah doesn't have to think of it that way. It could easily start with her not wanting to lose her toy and get his ass in a gym or some other activity to lose weight for his health, so he can be around for her. Which could lead her down the path you are discussing.
Technically she still hasn't humiliated Dan to his face or not like Lester has been wanting, so that's still a boundary to cross.