[breathesgelatin]

OK--so to clarify the record.

Alpha Delta Pi = first female secret literary society, 1851
Phi Mu = second female secret literary society, 1852
Pi Beta Phi = first national women's fraternity, 1867
Kappa Alpha Theta = first national Greek-letter women's fraternity, 1870
Gamma Phi Beta = first national women's sorority, 1874

Note that these are all NPC firsts. It may well be that

Phi Nu = first female Greek-letter literary society, 1853

but it does not claim to be national. Therefore, Theta is still the first national Greek-letter women's fraternity.

In sum:
Alpha Delta Pi, 1851
Phi Mu, 1852
Pi Beta Phi, 1867
Kappa Alpha Theta, 1870 (January 27)
Kappa Kappa Gamma, 1870 (October 13)
Alpha Phi, 1872
Delta Gamma, 1873
Sigma Kappa, 1874 (November 9)
Gamma Phi Beta, 1874 (November 11)
Alpha Chi Omega, 1885
Delta Delta Delta, 1888
Alpha Xi Delta, 1893
Chi Omega, 1895
Alpha Omicron Pi, 1897 (January 2)
Kappa Delta, 1897 (October 23)
Sigma Sigma Sigma, 1898 (April 20)
Zeta Tau Alpha, 1898 (October 15)
Alpha Sigma Tau, 1899
Alpha Sigma Alpha, 1901
Delta Zeta, 1902
Alpha Gamma Delta, 1904
Alpha Epsilon Phi, 1909
Theta Phi Alpha, 1912
Phi Sigma Sigma, 1913
Delta Phi Epsilon, 1917 (March 17)
Sigma Delta Tau, 1917 (March 25)