To get 8 inch squares, I added an extra "granny" row, and either a row of single or half double crochet, depending on the yarn. Some of this yarn is Red Heart, which required the single crochet edge, while the I Love This Yarn needed a half double crochet edge to make the same size.
To make her bow, I made rectangles of single crochet... 4 rows of 12 sc. Leave long ends to weave into the center, wrap around for the middle of the bow, and tie off at the back. Stitch into place.
Here's a picture of the scarf I made for my niece.