Photograph by Robert Maxwell “She wears heels,” says Bianca Casady (left). “I would never wear heels.” The “she” in question is her older sister, Sierra, the girlier half of the band CocoRosie. Sierra rocks out with slinky tops and beaded earrings to counter Bianca’s XXXL sportcoats and vintage spectators. “There’s a dialogue between our outfits,” Bianca says. Marrying their styles, inspired for the moment by drag queens, Jean Genet and hip-hop, means frequent trips to the dollar store. This was especially so while touring with Antony and the Johnsons for CocoRosie’s second album, “Noah’s Ark.” A sneaker fetish keeps Bianca on her feet. Fortunately, even in heels, her operatic sister has no problem keeping up.