Simply Summer Magic Top
This is a simple little top, sized to fit your little one's 18" doll such as American Girl Dolls. My doll seen here was a generic 18" doll, found in a catalog, and has the same proportions as the AGD (and seems to be a perfect match for the doll sold at Michael's).
It features slip stitch crochet ribbing (which can be replaced with single crochet ribbing, if you prefer), is worked back and forth in rows (but joined at the sides, so there's no seams) and the shoulders are joined with slip stitch crochet.
Thank you, testers: tdd, Tinochka7, agd509 and DonnaYB!