There is no black and white answer that anyone can give you. When chapters look at PNM's, most are interested in women who have done well in the classroom. Scholarship is an important aspect of the sorority experience.
I don't know about your campus, but on those that I am familiar with, women with lower GPA's generally have fewer options. The Texas State Recruitment book says that grade requirements vary chapter to chapter.
http://pc.dos.txstate.edu/how-to-joi...t-booklet.html
Good luck!