Question: What is the date of death of Dorothy Bush Koch's mother?
Sentence (from "Barbara Bush"): Barbara Bush (née Pierce; June 8, 1925 – April 17, 2018) was the first lady of the United States from 1989 to 1993 as the wife of George H. W. Bush, who served as the 41st president of the United States, and founder of the Barbara Bush Foundation for Family Literacy.
Relevant evidence: Yes