The oldest national sorority (I think) is Alpha Delta Pi (1851). Their Delta Nu chapter is
http://www2.semo.edu/adpi/chapterhistory.asp and founded in 1959.
The largest national sorority (I think) is Chi Omega (300,000 initiates), but they were founded only in 1895. No way were they prolific enough to get to Delta Nu by 1912.
Therefore, I definately think you are dealing with a local sorority.