As I write this, I am making the assumption that you want to join a National Panhellenic Conference Sorority (i.e. Women's Fraternity)

I think you would need to contact the Panhellenic Office on your campus and ask if you can participate in Rush. If they say "no", then you could contact the Headquarters of sororities that interest you and ask them about their "alumnae initiate" program.

I don't know anything about National
Pan-Hellenic Council sororities (i.e. they historically have "black" membership), but again, they must have an on-campus council, so if you were interested, your best bet might be to contact them and ask. If there are any NPHC ladies out there who could comment that would help. With the NPHC sororities, I have reason to believe that as a Grad Student, you can only join by invitation only. Perhaps if there are some NPHC ladies out there who could comment, this would be of help to you.

Good Luck to you.