What makes it sexy is her careless disregard for modesty. We just saw her naked in the last image, but now we want to peek under that skirt again.
Drawing transparent fabric is as easy as this;
1. Draw the figure, no erasing.
2. Draw some lines and shading for the dress.
3. Go over the raised portions of the cloth wherever there are folds and wrinkles with a white chalk
and Bob's yer Uncle!