I haven't gotten around to playing this one yet but it might be like the second game where every now and then you might see her character sprite doing a little sex animation in some corner of the map you can't reach and not any actual scenes.
So far, I've found 1 where she's doing something lewd on the same map as you: when she's in the maid changing room. But in that one, she's doing a specific sex act in the standing picture.
The other times, when she's changing or undressing (when she's in her bra and panties for example) don't seem to have a corresponding room or scene/sprite with them and she doesn't seem to actually exist in any location whether actually there or "there" because the system says so. For example, I had this one loop of the mansion where she was naked the entire time I ran from room to room of the mansion and didn't see her sprite at all. I don't remember if AGASE 2 was like this.
So it seems, that there's actually 2 types of standing pictures: meaningless ones, and real ones.
meaningless - she is in varying states of undress but that's it, no sprite or room scenes -> don't bother looking for here in this state.
real ones - she's actually doing some act or wearing something very situational like her bath towel. -> These exist in a location and have a scene or sprite with it.