Regarding "social affiliation", Pi Beta Phi does not allow it-according to our GC national officer--and I would doubt that many nationals do. Non-members aren't covered by our insurance and to quote her, it would be a risk management nightmare.
I can understand how a transfer would miss sisterhood--however, a few would and do ruin it for everyone. A local girl rushed at a large out-of-state university and was initiated. She transferred at the end of that semester and pledged another sorority at a smaller school. She was found out before her initiation and this was the reason she gave everyone for pledging again: "At my first school, we were the ugly sorority. I couldn't stand being thought of as a loser."