Forgot to tell you about my evil rho chi from hell!
It was very plain from the get-go that my PX was only doing it to get out of rush. She was never available for anyone in her group. She wouldn't give advice on outfits or anything. When I told her I was dropping out of rush, she didn't do anything to try to convince me to continue - she acted relieved - one less PNM to worry about.
At my school you weren't given advance warning if you were cut from all sororities - you showed up for your invites (or bid!) and instead your PX sat you down and told you you'd been cut. There was a girl in my group who got cut from every sorority before pref. She came away from her meeting with our PX bawling her eyes out. The PX made no effort to console her or anything, didn't even give her the chance to pull herself together, it was like "You didn't get any invites - NEXT!"
When I was a PX I swore I wouldn't make any of the same mistakes. I think I did pretty well
So, I second the advice of being available and approachable to all PNMs, not just those in your group, and if someone is cut from her favorite sorority, or all sororities, take the time to console her. Rush is very stressful and people overreact, and getting cut can seem like the end of the world.