You probably don't want to rent, but just to give an idea of some styles, because I think we have a similar body type:
http://www.renttherunway.com/shop/de...daisylacedress
http://www.renttherunway.com/shop/de...meetsgirldress
http://www.renttherunway.com/shop/de...firstladydress
The color is all wrong on the last one, though.
ETA: You said "big Greek school", but there is a big difference between SEC and Cornell, for example, even though both have big Greek systems, so I would like to be clear that I am a Big 10er, and you should feel free to ignore my advice accordingly.