My niece was turning nine, and I wanted to send her a gift. I've never met her, but my half-sister says she's into Barbie. Of course, the first thing that came to mind that could cross over between Barbie and what I like is: a dress! I always wanted a big poofy dress for my Barbie, but didn't get any until I was kinda getting out of playing with them anymore.
I started with a tiny hoop skirt, boned with plastic boning, and did a dress out of real silk. I had the silk scrap around from when I was choosing fabrics for my wedding dress, and real silk was going to look so much better at small scale than polyester. It still wouldn't drape how I hoped it would, but it's pretty good.
The back snaps up. And the inner seams are fused with interfacing so they don't fray.
If I were to do one again, I would simply interface the whole section the bodice pieces were going to be cut out of before cutting and sewing. Both because ironing the tiny seams was a pain, and also to stop the silk from stretching and causing the ripples on her sides. It would have fit her better.
I don't really go for puff-sleeves myself, but they work for Barbie.