Realistically, we are looking at two separate pieces. The apron would be meant to come off if dirtied during a day’s work and easily retied. Looking at the back of the apron suggests that it would not be such a quick task to replace so it’s not a big deal if you choose not to separate the two pieces.
The musical is the best reference for details, but please note that some details have been made larger in order to be seen on stage. A good example of this is the bow at her neck. It doesn’t need to be that big. But it’s a good reference for the lace on the hat, etc.
This concept art from one of the artbooks is the best all-around reference.
The apron is made out of a white, sturdy fabric; probably a medium-weight cotton. The skirt sits under the bust. There are four large navy buttons (fabric-covered is a good option) in front that appear to be for decor only.
On the sides are two straps that go up, with ruffles over the shoulders and around the back. They then lace the back of the apron’s skirt. The large bow probably just snaps or buttons on. There is no realistic way it could be part of the strap. It would then hide the laces.
The dress is navy and also probably a plain, sturdy fabric. NOTE: the colour in the musical could be interpreted as black. Your choice. The white cuffs fold up and widen as they do. There are three navy cuff buttons. I’d also guess they’re fabric-covered.
The top looks more complicated than it is. The white and the blue ARE part of the same piece but if you prefer you can have it be a separate undershirt or dickey. (It will just slide around so not overly recommended) Note how high the collar is as well as the fact that the buttons in front are fake (three matching the cuffs). The four buttons in back are real.
Don’t forget petticoats under these skirts. It will not poof out if there are no petticoats. (Hoops are likely to be unnecessary though)
She wears over the knee socks or thick tights in black with brown lace-up boots of a sturdy nature with no real heel. (Wear whatever is most comfortable with your petticoats) The laces must be too long for her as she ties them around the top of the boot to shorten them.
I’ve tried to do some research on it and the best I can explain this is that it’s made like a lolita headband or headdress like this: LINK. And then in back you have more white cloth that covers the high pigtails, probably in a full half circle shape. I’ve been unable to find a pattern that matches this precisely, but this should be a good place to start.
The musical’s headdress is bigger than the one in the manga. Use your own discretion in how over the top you want your outfit to be! Definitely use some good lace, though.
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