Does your sorority have wedding traditions? I'm a Kappa Kappa Gamma, and we have a song called "Oh Pat" that is sung at weddings. It's a fun, lively song, and all of the Kappas usually make a circle around the bride and groom (or just the groom).
I've also seen brides borrow their sisters' pins to either pin inside their dress or on their bouquet. I've seen this for other sororities, too. (Yay, Pinterest!)