Pennsylvania Ballet soloist Abigail Mentzer is a dancer's dancer. On top of her innate sweetness and lyricism, she also makes all the girls around her look good—in her handmade skirts. What started as a hobby four years ago has blossomed into a lucrative side business. This fall, Capezio's flagship store in New York will sell her Abigail Mentzer Designs in a trial run. Her skirts have done for dancers' bottom halves what Yumiko leotards did for the top.