I would think at such a small school you may have a shot at getting a bid despite your senior status...especially if you explain that to the chapters/have your rec writers include it (if you get recs). I know some may disagree, but I have known girls who pledged their junior or senior-with-a-year-and-a-half-to-go year and still got an AMAZING experience out of sorority membership. You just have to ask yourself whether you think it would be worth the financial and time commitment you would be binding yourself to for just one to two years of collegiate experience--the lifelong alumnae membership notwithstanding. Generally, one's senior year can be their most time-constraining academically and you would be incorporating new member classes, chapter meetings, required events, etc. into the mix, so you will just have to evaluate those things and come to the conclusion that is best for you. In any event, good luck with your decision and I hope that you have a great experience!