Do you want a pattern in a girls' size or a misses' size? Either way, there are plenty of patterns that would be close, as it looks like a pretty simple dress.
Two front pieces: bodice with a notched or v-neck, and a skirt, with the seam just at the waist, the back is probably three pieces, as it looks like it laces up the back in one picture. It looks like it has some wide trim at the hem in a darker purple than the dress. The sleeves are cute—they remind me of the ones on Lucy's blue Narnia dress... but these are open almost to the elbow, with the corners rounded. A bit petal-like, almost.
Hee, who knew we'd get another girl character in costume?
That's one positive, even if the addition is making me nervous...