OK, how do you like the shape of this one in general? I realize it will be too big.
But it is basically a rectangle. Have your daughter stand up with her arms out straight side to side. Measure wrist to wrist, going across her back. That's how long you need to make the rectangle. They do have some increases along the sides, which you can do or not. If you want the increases, yu might want to increase every 6 rows instead of their 10 rows. When you get to the halfway point or center of her back, start decreasing down to he original number you cast on. The pattern is starting out by casting on 25 - you will probably need fewer. Measure around your daughter's wrist, add a few sitches and cast on that many. This will depend on the guage of the yarn you are using.
Hope this makes sense - it is so clear in my head, maybe not so on paper!