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 his legacy.
In May 1954, Diane married Ronald William Miller and 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. 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 her mother but got bogged down in wrangling over costs. She ensured the original design by Frank Gehry went ahead, and it finally opened in 2004.