Frozen Fever Anna – Halloween

My 4yo goddaughter has picked this year's Halloween costume - Anna from Frozen Fever. 2yrs ago she was "Baby Anna" and I heavily altered a Fairy Tale dress to get the look I wanted. I'm not sure what will work best as a starting point for Frozen Fever Anna - I was considering the Fairy Tale again just because I love the fit. Would it be easy enough to change the collar to a band collar style? I want this to be an all in one dress with the look of the shirt/bodice/skirt/vest. I have an embroidery machine and I can design the embroidery part myself...or my mom can! ;-) I'll probably use cotton broadcloth and make it super sturdy - she wore the last one for 2 years! Any tips and suggestions are welcome! I've done some googling and get cosplay ideas. I want it to look like Frozen Fever Anna but it doesn't have to be an exact replica - she is four and should look like a 4yo in the dress!