Melissa,
The Panhellenic Council on your campus, which is the governing body for all sororities, should set a minimum GPA to participate in formal recruitment. On my campus I believe it is a 2.5. In Kappa Delta, the average GPA of our whole chapter has to be above the All Women's Average at our school. Basically the chapter determines the GPA, it can vary from chapter to chapter.
Also, feel free to visit our national website:
Kappa Delta Website
P.S. Any sisters can feel free to correct me if I'm wrong, I don't have a COHB or Norman Shield around