That's cute and I've made her sweaters before. They seem to be well written and easy to understand. The yarn used in the projects seem to be a variety of mostly worsted weights and even a few DK's. I looked to see if anyone said anything and one using DK just went up a size. There is probably more info as well.
The yarn they use is a heavy worsted weight (#4) at 16 st over 4 inches..that's 4 spi. Check the yarn you want to use and see what the gauge is. You can check on Ravelry for that, too. What yarn is it you want to use?