Bridal Party - When the Best Man's a She Instead of a He?

Q: My fiance wants to have his sister as his "best man." As much as I hate the idea, I know it's becoming popular. My question is, how should she dress? Like my bridesmaids or like the other groomsmen?
-Stacy - Washington, DC-

A: Etiquette is still evolving around this new twist in gender roles, but whatever you do, please don't put her in a tuxedo. And give her a corsage, not a boutonniere. The idea here is to give your future sister-in-law an honored part of the ceremony, not to pass her off as a guy, no matter which side of the aisle she stands on. General rule: The groom's female honor attendant can wear a gown similar to your bridesmaids' dresses or a pantsuit of the same color.
-Cori Russell - Style and Etiquette Editor, Wedding Expert -