I like her dress!! It seems to be composed of my two favorite time periods in history. The skirt is a modified Victorian ball gown skirt but the bodice appears to be a stylized French Rococo type (its because of the collar shape).
I thought that as well because, Disney tends to use the same mix of styles but with more simplified details. A great example is Cinderella which features a mix of late Victorian and the Tudor practice of using different colors that compliment in different layers.