stepsister black balling?

No.... Maybe in that particular sorority, but she can't black ball you to other sororities. No sorority would listen to that. Trust me, it's a lot harder for actives to drop a pnm than you think it is.

If she is currently an active in the Alabama chapter then yes, you probably have something to worry about, but only for her chapter. Check the national website for her particular sorority and see what it says about legacy status. Some consider step-moms/step-sisters legacies if the sorority member considers the PNM to be a legacy (since sometimes the step siblings/mothers-daughters don't have a good relationship). If she is an alumni of the Alabama chapter then maybe...but if the sorority likes you then they probably won't listen to what one girl says if all the things that other people say about you are positive. And if she is an active member/alumni of a chapter at a different school, then I'd say you have nothing to worry about.

Could you reach out to her and have a heart to heart? Maybe if you and your SS could talk she would realize that you were effected by this situation too, and that you have a lot in common, aside from the blended family. I think it is worth a try.