For the skirt part, google lolita rectangle skirt tutorials like this
. I would then just shorten the skirt to the length you need, add any detailing you need, add a correct shape petticoat (I know she doesn't wear one, but you can't get poof without one), and viola. You can then draft sew in under sleeves instead of making it all one piece so it won't be as hot. You can also find bloomers like that cheap on sites like Bodyline.