Here are some excellent resources for exploring more about Willa Cather's life and works. The archive at the University of Nebraska - Lincoln where she went to school looks like a treasure trove.
http://cather.unl.edu
http://www.willacather.org
The archive has published online scholarly editions of her works. The quality of these are fantastic. The illustrations and explanatory notes are a great supplement!
http://cather.unl.edu/index.wcse.html