Who Is Lucy Herr and Why Is She Living with My Great-Grandfather?
According to the 1920 census, Mary was married and living in Chelsea, Oklahoma with some of her children, but not her husband. David was widowed and living in Oklahoma City with his "half-sister," Lucy D. Herr. Unless there is a long-lost family secret, David didn't have a half-sister.
From what I have been able to gather to date from censuses and her obituary, Lucy Deere was born in 1865 in Oregon to Mary and William Yates Deere. Her parents died when she was a child. She was a great-niece of John Deere of farm equipment fame. She was an artist, but also worked as a servant and a courthouse records researcher. She first married Don Alexander in Oregon and, after his death, Benjamin Herr in Oklahoma City. According to her obituary, "Sixty years ago she was in the headlines when John Mulvaney (sic), painter of Custer's Last Rally, committed suicide in New York, purportedly over his failure to win her love."
David and Mary Donaldson were again living together at the time of the 1930 census and Lucy Herr was back in Oregon. She later moved to Sacramento, where she died in 1946.
So, what was the nature of their relationship (I know what you're thinking, but I'm trying not to make assumptions), what brought them together, how long were they together, and why did they part ways?