This plaque, dedicated by the Nebraska Federation of Women's Clubs, was finished in 1950. Its relative proximity to the time of her death makes it seem like the memorial least motivated by the author's fame alone.
The halls were named only a few months before their completion(Minutes, Board of Regents). While no reason was discussed by the Board of Regents, two other halls (Abel and Sandoz) were under construction at about the same time, and this suggests a rush to choose names for the halls. The naming was likely arbitrary.
The garden was first suggested in the centennial year of Cather's birth. This is evidence toward a general awareness of her and the work she did, which would have been prevalent in that year.
Again, an awareness brought on by the centennial (this time of her graduation) likely spurred the donation of this memorial.