In the book, the only description for Rapunzel's dress is that it is green and yellow and embroidered with wings. I rented a costume to take pictures of, and it had sleeves like this. Thanks for noticing!
Weird thing- I read this book as a kid and really liked it, and over the last week or so as an adult I've been thinking "Man, I should really reread Zel, that was a good book." Clearly, seeing this piece is a sign. And it makes me super happy in my soul. :3 That DRESS is just amazing- the slashed sleeves have such great dimension to them. Beautiful work, and congrats on the DD!