I was a rho chi for my senior year. It's so rewarding to see your charges go running off to their new homes, whether or not it's your sorority.
You will have to be prepared for anything: PNMs cut before pref, PNMs who attend pref and then are not matched, PNMs who get their second or third choice and are upset.
I had a very insensitive rho chi who told one of my fellow PNMs, "You didn't get any invites to pref, NEXT!" The PNM walked out of the room crying in front of all the PNMs waiting to hear about their invites (including me).
My advice: Make sure your PNMs know how to get hold of you by phone and email, and give them accurate advice as to how to dress and what to expect at each round of recruitment.