There are several threads explaining this, started by CutiePie2000, I believe.
Basically, alumnae initiation occurs in NPC groups for women who were not in a sorority (or an NPC sorority, to be more exact) in college. Either they seek out the sorority, or women in the sorority who they are friendly with seek them out. The process varies greatly from sorority to sorority. I would say DG, Alpha Phi, and Gamma Phi Beta have really been pulling in AIs, just based on what I have seen on GC. I know in Gamma Phi we are putting a big emphasis on it and it has been featured in our magazine, as it was in DGs, when our very own DGMarie wrote the article!
Some cases where women I know are seeking or have sought out AI:
- Our chancellor's wife at my chapter of initiation. When we were a local in the 1950s she was our president, campus homecoming queen, etc. It was awesome to see things come full circle and watch her become a Gamma Phi Beta.
- Our Greek advisor at my chapter of initiation - she never went Greek in college, for whatever reasons, and we thought a Greek advisor would understand things better if she was Greek herself.
- My mommy, very slowly!
She put herself through Marquette, which is a relatively anti-Greek school, and so never had the time or money to be involved with a sorority.
- A woman I know who just graduated who never rushed in college because she thought you had to be invited.
We can't really discuss initiation procedures, for obvious reasons, but I think it is safe to say that everyone is initiated with collegians, from what I've been able to tell on GC.