Purdue Panhellenic's set of FAQs for this fall's formal recruitment is in PDF (Adobe Acrobat needed) at:
http://www.purdue.edu/greek/reports/...itment_faq.pdf
As to recommendations, the FAQ page says they are not required by Panhellenic but some sororities use them.
Actually, of course, some sororities (not all) have national policies stating that a woman
must be "sponsored" (or some other word indicating a recommendation of some kind). In theory if a sorority chapter is really interested in someone, it will manage to get a recommendation or "sponsor" for her. Now, on planet Earth, if there are hundreds of women going through recruitment -- and if, as at Purdue, the timing and details of the formal recruitment process are new to everybody this year -- a sorority may not have the time and energy to put into tracking down a recommendation or going through a special process to make sure someone is "sponsored."
So my guess is that it would be a good idea to try to get recommendations to as many of the Purdue sororities as possible.