actually the reading that mrs de winters achieves a perverse form of catharsis by being subsumed into the mother role is so interesting to me.
you have mrs de winters describing a (desired at the beginning, and achieved at the end) deeper form of partnership as being closer to a mother to maxim, her child. the way in the pivotal moment (when maxim breaks down and confesses the murder) there is a complete role reversal: maxim is not in control anymore, while mrs de winter is the driving force behind their scheme (ie. she is committed to perjuring herself; its her intervention that prevents maxim from losing his temper when questioned). plus, during their 'exile' post the manderly-fire he is a broken man, and she is taking this caretaker, motherly role, by managing his emotions and dark moods like a toddler.
and i will also point out how rebecca's final diagnosis explicitly establishes that she could never have borne a child due to a deformation of the uterus, aside from the cancer that would have killed her.
so, in a way i would say that's why the rship with maxim was never true companionship, and that's because she could not be his mother. while mrs de winter can and does!