@liszst idk your gender alignment but you'd sure fit the bill of a control-freak-spouse.
the heroine had already suffered both physical and mental abuse to the point that her coping method could only ease her symptoms even after selectively forgetting pretty much her whole life.
based on her current state, firmly
asking her to lay down (
politely as you so put it) would probably be effective but only in the sense that she would treat it as a command to be obeyed by a slave.
this goes completely contradictory to the goal of the ML for her to develop a backbone of her own if almost everything she does, aside from cowering in fear, needs to be first dictated by him,
the Head of the House.
the
forced princess-carry that you claim is simply for shoujo-fanservice, however, would actually serve a far greater purpose in her rehabilitation.
based on her current condition, sure, it would cause her to be swamped in confusion and fright. but that is only because the concept of being treated kindly by others is still foreign to her. the prison aside, she is still under the assumption that the staff of the estate are only nice to her because they "incorrectly" saw her as a guest of the lord's and not the worthless slave that she believes herself to be; heck she was even scared when the other servants tried to help her out.
as such, no matter the approach, any kind gestures would only cause her fright and discomfort initially and this type of occurrence is precisely what she needs on a frequent basis to even
start to get the notion of redeveloping a sense of self-worth.
so based on that situation, for ML it was a choice between (A),
asking her to lay back down and reinforce her suspicions that she is his "property", and (B),taking the initiative to lay her down so that later, she might begin to wonder why he did that
for her.