Diane was a noted philanthropist. From her father's death until her own, she donated nearly five million dollars to various charities within the United States and devoted herself to preserving her father's legacy.
In May 1954 she married Ronald William Miller; they had seven children. In the early 1970s the couple purchased a vineyard in Napa Valley, California. Starting in 1981 they operated the Silverado Vineyards Winery on a tract of their Napa property. Ron Miller was CEO of The Walt Disney Company until 1984, when Diane's cousin Roy E. Disney supported Miller's ouster in favor of Michael Eisner and Frank Wells.
Diane was instrumental in pushing ahead with the Walt Disney Concert Hall in downtown Los Angeles. The project was initiated with a $50 million gift from Lillian Disney but got bogged down in wrangling over costs. Diane ensured the original design by Frank Gehry went ahead, and Walt Disney Hall finally opened in 2004.
Her memory was dedicated in the 2013 biography film Saving Mr. Banks.