did she ever actually "sleep over"?
One time comes to mind -[spoiler]when she was taking care of Joe.[/spoiler] But Barnabas wasn't even home for much of that time because [spoiler]he was off being instructed on how he was to kill Joe by dispensing the poisoned medicine.[/spoiler]And I don't think Willie was supposed to be home either - though I have no recollection of where he was supposed to be or even if we were told. Though even at all that, thankfully Julia slept in a chair in the drawing room.
so that the impression is not left to the audience that joe and maggie slept together
Joe and Maggie actually sleeping together?!
The shock!! The scandal!! The scene of the townsfolk dragging Joe out into the town square for an immediate tar and feathering - and then running him out of town on a rail!!! Not to mention the shunning of Maggie by all "good and decent" people from that point onward - even without a scarlet letter sewn onto her Junior Sophisticates.