You could do "DG and the City".
I'd avoid the 50's theme because it could come off more cutesy than sophisticated. And I'd avoid the Aladdin theme unless everyone could pull off a sexy little Jeannie inspired outfit.
With "DG and the City" the chapter can dress in chic or trendy clothes and have a skit about 4 very different rushees and thier search for the perfect sisterhood.
And you can use the city supplies that you already have!
You could also do "Studio DG" ala Studio 54 or a coffee house/poetry reading/beatnik theme