The current Professional Fraternity Association was formed in 1978 from the Professional Interfraternity Council (PIC) and the Professional Panhellenic Association (PPA). (The first being the ones which were men's groups, the second for women's groups.)
I've found that Alpha Sigma Alpha was a member of both the Association of Education Sororities (The AES merged with the NPC in 1951 bringing in the last large group of Sororities into the NPC) and the Professional Panhellic Association at least in 1943
http://issuu.com/alphasigmaalpha/doc..._no_4_may_1943 (page 39).
The other original driver in the AES was Sigma Sigma Sigma. What I'm trying to find out is whether Sigma Sigma Sigma (the organization in the NPC today) was one of the chartering groups for the Professional Panhellenic Association in 1925. One of the charterers for the PPA is called Sigma Sigma Sigma, but I'm not totally sure that it is the same group The group in the PPA was listed as having an emphasis in Education which would certainly fit with the now NPC Sigma Sigma Sigma being in the AES...
An additional piece of information the January 1944 copy of ASA's Phoenix
http://issuu.com/alphasigmaalpha/doc..._no_2_jan_1944 (page 13) had a report from the PPA's 11th Biennial Convention. That also includes a mention of a Leader of Sigma Sigma Sigma running the Alumnae contacts email. But I'm still not 100.000% sure that the Sigma Sigma Sigma in the AES with Alpha Sigma Alpha is the same one that is in the PPA with them.
(And one way or another, I wonder how much overlap there was between the PPA and AES)
Any ideas? I'm considering calling Sigma Sigma Sigma headquarters tomorrow (Tuesday) morning...