The costume appears to be inspired heavily by the (late) Victorian era, but doesn’t fit into any particular style from that era. I’m seeing puffed sleeves, a full skirt (likely based on a circle), and a high-necked bodice with a bib. Due to the very simplified and stylized artwork, you have a lot of leeway when it comes to exact details, which you can use to your advantage.
Here are a few ideas, though all of these will need modification of some sort:
This Edwardian pattern, without the skirt trim or the longer sleeve portions
This pattern is vintage and may not be available, but it would be a good base in terms of shape
You would need to add a bib and shorten the sleeves, but if you don’t mind the button front (or know how to change it), this pattern has a very good shape
If I were you, I’d sit down with the pattern books at the local fabric store and flip through them. This is what I would focus on:
– The overall shape and silhouette (skirt shape in particular)
– The sleeves (do they have the fullness you would need, or would you need to modify them?)
– A bodice that isn’t overly shaped (no boning or other heavy shaping and structure)
– Skirt sits at the waist
– Preferably a high neckline
Once you have a pattern (or multiple patterns you’re combining) with these elements, the rest is relatively simple to modify or add. If you get a pattern with a vastly different shape or silhouette, however, you will have a much harder time trying to get it to do what you want.
As for the hair, I read it as being very curly with side bangs. You can curl a wig yourself, though I think that the Nicki from Arda in Ocean Green would be nearly perfect out of the bag – you’d just have to change the bangs a bit.
I hope that helps! Good luck :]