I was able to locate one small alumni file for Ralph LeMaster, but nothing about Mary. This is pretty common with students who only attended the college for a short time, especially in the earlier days of Oberlin.Ralph's file contains a few address cards (most of them contain the same address: 213 E. Rush St, Kendalliville) and a nice alumni questionnaire sheet. These sheets would have been sent out by the college for different purposes, mostly to keep records updated about alumni. This was filled out by Ralph in 1922, while he was still a student at De Pauw.
The archivist's fiancee has a grandmother who was a LeMaster as well. She's passing on to her future m-i-l about the blog, and I'm still looking for a connection.