I would imagine that all 26 NPC sororities allow married women to pledge. I would also imagine that certain chapters of all 26 NPC sororities have probably have pledged some married members at some point. However, that doesn't mean that AB chapter of XYZ sorority at SEC school will offer a married PNM a bid.
Like others have said, at the competitiveness and more importantly the tradition of the campus. You mentioned that you have a good college GPA, and are involved on campus, so that means you wouldn't be going through as a freshman. At some traditional competitive campuses, merely being a sophomore will be a detriment, nevermind being married.
Reflect on how much time you have or what you are willing to put into a sorority. Are there activities (such as going to fraternity mixers or serenading) that you would find objectionable? How late are you willing to stay to work on your chapter's Greek Week skit? The time commitment required will be different from school to school and chapter to chapter. Can you meet the minimum requirements? Are you willing to go beyond the minimum time requirements?
Sororities want members who will participate in all facets of membership, members who will volunteer for non-required commitments, members who will lead, and members with whom they can relate and develop lasting friendships.
My little became engaged when we were juniors (she joined as a sophomore and we both just graduated), and the chapter was incredibly happy for her. We had a candle passing ceremony for her.
She spent (and spends) a lot of time with her fiance but she remained active in all aspects of our chapter.
Depending on the campus (after all we don't know if you are going to an SEC school or a smaller less competitive and less traditional school), you may have a serious uphill battle to get a bid. Talk about why you want to join a sorority. Tell them what you have to offer. Address the concerns that myself and other GCers have brought to light. We can't really tell you what kind of shot you have at this, since we don't know your school, and it is in your best interest to remain anonymous. Just remember, just because sororities CAN bid married women, it doesn't mean they will.