unwashed gauge: 26 st / 41 rows = 10 cm
washed gauge: 27 st = 10 cm

I followed the stitch counts for size M, aiming for a size S dress.

Dress length 60 cm. With my gauge, the ribbing in hem is 5 cm. Same for waist ribbing. That leaves 26,5 cm for the decreases. And 23,5 cm before decreases.

I added one extra row between each decrease, that seemed to correspond to the original decrease pattern well enough.

For sleeves, I changed the increases a bit: first incr. row as in the pattern, second after 4 cm with only half of the increases, and a third 2,5 cm after that with the rest of the increases.