Mods:
I CO 128 st with the size 4 needle and used this tutorial for the brioche stitch: http://www.purlbee.com/brioche-stitch-in-the-round/

I knit the skirt until I ran out of white yarn (100 g), then changed to the 3.5 mm needle and worked rib (k1, p1) in main color. I continued in the round for 9 cm before dividing for armholes.

The dress is quite long, so I guess it will fit her next winter as well!