This is a cute jumper of Molly's that she wears a couple times in the movie.
I cannot tell whether there are one or two darts on either side of the bodice.
I can't tell what kind of fabric this is, but I really like it. :-)
She wears a belt with it, as you can see:
Here's a view of the skirt.
I think this dress might be constructed in a similar way to Molly's plaid jumper, dissected here at In Timely Fashion.