I am an SDSU Sorority Alumna
Correction: last year quota was in the mid eighties for SDSU. I know that my sorority would have been open to an exchange student, however, Sigma Kappa closed in April of last year.
If you are really interested in joining a sorority, the Fraternity and Sorority Director may allow for you to join and for you not to count towards quota. There is always COB'ing, which tends to be less competitve.
Here is the link for SDSU Greek Life, I say definitely look into it. Joining a sorority is a great experience!!
http://www.sa.sdsu.edu/cfsl/