Audrey’s character makes her escape from the palace in the dark. It’s not the most practical outfit for climbing out of a palace in, but then she is a princess! :)
Button up white shirt and skirt with wide belt:
The skirt is so full it look like it may be a full circle:
Close up of the blouse. See the little pin tucks at the shoulder. There does not appear to be a sleeves seam- are those kimono sleeves? The scarf (or jabot) at the neck turns out later to be detachable, and also appears to be pintucked?
Back view. What a wide belt!
First meeting with Gregory Peck’s character:
Getting ready for bed. Off comes the jabot:
Undoing the wide cuffs on the full blouse sleeves:
Off with the skirt! And underneath is a petticoat to give the skirt that fullness. It has a hip yoke for a smooth line over the hip: