Here's the website for clubs at Duke:
http://www.duke.edu/org/org.html
they include:
Alpha Delta Pi
Alpha Epsilon Phi
Alpha Omicron Pi
Alpha Phi
Chi Omega
Delta Gamma
Delta Sigma Theta
Kappa Kappa Gamma
Sigma Gamma Rho
Zeta Phi Beta
There were others but these were the ones I recognized as being sororities. There were a couple special-interest organizations as well.
When it comes down to it, the best sorority is going to be the best sorority for HER. Encourage her to give each organization a chance, and go with where she feels most comfortable. That's the sorority where she'll do the most good, feel most involved, and get the most from.