I have made a few disney things including sailboat Mickey pants and skirt (red with just two big white buttons). I thought it worked well, mickey was originally a sailor after all right? I know she doesn’t like minnie, but I also made a minnie dress with the tea party pattern (http://www.flickr.com/photos/59555784@N02/8452468313/) I was just thinking it might work for a very simple rapunzel dress because you could add contrast piping and a different shade of purple for the center panel to mimic the overlay effect of her dress.
My little girl loved Cars the first time we went to Disney and of course it is NEARLY impossible to buy anything Cars for girls so I made this Little Lisette dress for her: http://www.flickr.com/photos/59555784@N02/7154995476/ You could do something like that with mickey fabric too. I also made her a simple tiered ruffled skirt out of Cars fabric. http://www.flickr.com/photos/59555784@N02/6807019921/
Good luck! I had planned to sew for our trip last year, but only got one outfit done for each of them. Good that you are planning so early though because those deadlines always seem to creep up!